Cross-posted to the Courage Campaign's Prop 8 Trial Tracker.
As I do this sort of flash analysis, I want  to start with a big,  broad, general point here. Namely, while you can  see possible avenues  and ideas that may filter into a decision,  focusing on “winners” is a  sucker's bet.  Perhaps, if you take all the  questioning as a whole, you  end up with some tougher grilling of the  opponents, but judges like to  play devil's advocate.  Sometimes you can  get a read, and sometimes you  can't.  Also, I haven't really had the  time to fully analyze each aspect of these arguments, so forgive me if I  misread, or am just plain wrong, in places. 
So let's take a look at the meat of the issues, and see what we learned today over the flip
Imperial County
The  attorney for Imperial County, and Isabel Vargas, the deputy clerk  of  the county, took a real beating in the courtroom.  Robert Tyler, of  the  Advocates for Faith and Freedom, a right wing anti-equality   non-profit, came to the podium in front of a skeptical panel.
First,  the court had an issue with the fact that the actual clerk of  Imperial  County was not a party to the attempt to intervene. Rather, Mr.  Tyler  represented Ms. Vargas, who only really has authority to act as  an  agent of her elected boss, Dolores Provencio.  Erwin Chemerinksy, the   Dean of UC-Irvine's new law school, had this to say about the oral   arguments:
If Imperial County can intervene and  defend Prop. 8, then there would  be no need for supporters of Prop. 8  to have standing to do so. But  both Judge Hawkins and Judge Smith seem  very skeptical of the authority  of the deputy clerk to seek to  intervene on behalf of Imperial County.  Both stressed that the clerk is  not seeking to intervene and a deputy  clerk lacks the authority to do  this. Judge Smith also has raised the  issue of whether the clerk is a  state officer or a local officer. If the  clerk is a state officer, then  the clerk would not have the authority  to represent the state — only  the governor and the attorney general can  do so. The clear sense so far  is that all three judges are very  skeptical of allowing Imperial  County to intervene. (LA Times)
Of  course, the question of Imperial County really only becomes  important  if the Court decides that the proponents do not have standing.   But the  Imperial County claim looks like something of a long shot at  this  point, or at least not something you would want to be pinning your   hopes on.
Standing of the Proponents
This  is where some unexpected wrinkles came up in the oral arguments.    Namely the possibility of the “certification” of a question to the   Supreme Court of California.  But let's back up a step.
In the  questioning of David Boies, Judge Smith (the lone Republican  appointee  on the panel), asked him whether the failure to defend Prop 8  was a  “nullification” of the efforts of the proponents and the choice of  the  voters in a way that was akin to a “veto” by the elected state  leaders.   Of course, a veto of an initiative is not allowed under the   Constitution.  So,.conflict? (Here's where I'm hearing an ominous   duh-duh-duh in my head.)
Well, not really.  Boies points out that  the California Supreme Court  was in fact asked whether Brown and/or  Schwarzenegger were legally  obligated to defend Prop 8.  And, in fact  they were asked by the  “Pacific Justice Institute” exactly that  question.  PJI was first denied by the the 3rd District, and later by the California Supreme Court.
There  is a process for appelate courts to ask state courts a question  about  state law, called certification.  Basically, they “certify” a  question,  and the state supreme court can answer it.  It would delay the  process  substantially, and given the quick dismissal of the PJI attempt  to get  Brown to appeal, doesn't really seem either necessary or  worthwhile.   Essentially, the state supreme court has spoken on this  issue by  failing to force the appeal.
However, if the panel really felt  strongly on this subject, they  could go to the State Supreme Court.  We  would probably here about that  fairly soon.  But, really, don't expect  that.
Returning to the main issue, the ball game was essentially played on the field of Arizonans for Official English, with   various cases modifying it.  The court was essentially trying to  figure  out if there a) had ever been a case where a proponent was  deemed to  have standing and b) if this should be that first case.
Charles  Cooper, the attorney for ProtectMarriage.com, eventually  relented that  there was not such a case. However, he then went on to say  that the Strauss decision,  where the state Supreme Court  upheld Prop 8 was an example of just  that in the state court.  There,  Brown and Schwarzenegger once again  refused to defend, but the  proponents had standing as defined by the  California Supreme Court.
Now, Article III standing isn't the  same thing as California  standing, there is different jurisprudence on  that. However, the  admission that there was no case makes the  proponents request a question  of novel law.  Now, that's not to say  that they can't win on this  question, but it does underscore the big  question mark on this issue.
The Substance
After  all the process of the first hour (plus 15 minutes), it was on  to the  meat and potatoes of the due process and equal protection claims.   One  interesting initial point was that both sides seemingly dropped  the  question of intermediate or strict scrutiny.  Ted Olson briefly   mentioned that he think that it could apply, but the substance of his   remarks all stuck to the question of whether there was a “rational   basis” for Prop 8.
I think there were a couple of specific points that attracted most of the attention, the Romer case, and this question of the “word”.
The “Word”
Judge  Smith focused a couple times on whether the State of California  was in  a worse position for having passed Prop 8 because it has given  all of  the same rights and privileges under the auspices of the domestic   partnership statute.  In other words, if we are only fighting over a   word, and no substantive differences at the state level, aren't we   essentially creating a subclass?  And roughly transcribed, here's what   Cooper said:
Cooper: The word is the institution. If you redefine the word, you change the institution. 
I  actually think this was a big moment of the oral argument.  It said   that yes, the anti-equality forces were there only to “put down” gays   and lesbians, or as San Francisco Deputy City Attorney Therese Stewart   said (again, this is my rough notes here)
If the word is the  institution, then the argument is just that gays  and lesbians would  “Stain” the institution. The fact that Prop 8 is  symbolic, it makes the  insult obvious. This is classification for its  own sake, and it  violates the equal protection clause. Taking these  components together,  it infers animus.
If we only passed Prop 8 to show that same-sex  couples aren't as  good, or as worthy as other couples, then isn't the  equal protection  argument plain to see? It reveals the naked schoolyard  taunting aspect  of Prop 8.  Nah-nanny-boo boo, you aren't as good as  me.  And frankly,  nanny-boo-boo isn't a valid use of state authority.
Roemer
Romer v Evans struck   down Colorado's Amendment 2, which barred local governments from   recognizing gays and lesbians as a protected class, as the City of   Denver had done earlier in the decade.  In the decision, Justice Kennedy   said that the law denied LGBT Coloradans the protection of the law in   an impermissible way.  It was so broad as to “confound” judicial review   and that Amendement 2 was raised of animus.  Or as Kennedy put it:
[L]aws  of the kind now before us raise the inevitable  inference that the  disadvantage imposed is born of animosity toward the  class of persons  affected…
Cooper argued that the legislation at issue in Romer was  so broad that it couldn't be constitutional, whereas this was just  one  issue, the word “marriage.”  Judge Hawkins pressed Cooper, saying  that  the removal of rights, especially this right, put it back in the Romer  territory.  This issue of the removal of rights looks likely to come up   in the decision, if the court does reach past the question of   standing.  The question just seems to large, and too conflicting with   prior law, to not be a major part of the decision.  And generally,   that's a good thing for equality.
Who wins?
So,  can we predict a winner from the argument today? Well, I go back  to my  initial statement, it is hard to tell from an oral argument alone.   If  you really pushed me, I would say that the plaintiffs would be the   favorite at this point.  The duel questions of standing and whether the   court could really find a rational basis hang in the air.  And I'm not   sure that Cooper satisfactorily answered either.