Obviously right now the issue consuming the most attention is who will be Obama's VP. The conventional wisdom is that it is going to be Joe Biden. I am not so convinced. I think Obama is supremely confident in himself and his campaign. It has been clear for a long time that he has a plan and he is going to stick to it. That being said, I think he will go with the person he is most comfortable with.
The thinking behind Biden is that he would help shore up Obama's perceived weakness in national security and be a great attack dog. However, I think Obama is not thinking that way. He has made it clear that he is confident in his ability to handle foreign policy and does not view it as a weakness at all and that the primary criteria for his selection is going to be someone who he can work with, agrees with him on his "new politics" philosophy.
If I had to guess who his pick is going to be I would put my money on Gov. Kathleen Sebelius of Kansas. Picking her fulfills all of the criteria listed above and all the criteria Obama has laid out to the press for his VP. Moreover, of all the names on the supposed "short list" Sebelius is the one that Obama, as has been reported repeatedly, is the most comfortable with and gets along with the best.
Now, the Clinton lovers will probably go ballistic over this pick but I view that as an added benefit to picking Sebelius. Obama has made it pretty clear he has bent over backwards to accommodate the Clintons (prime time convention speaking slots, roll call votes, the stupid statement in the party platform about the "18 million cracks in the glass ceiling", changing portions of his health care proposal to reflect the Clinton plan, helping Clinton retire her debt) and, up until now, he has gotten little to show for it (see Bill Clintons statements re: qualification for president, compliments regarding John McCain's environmental record). By picking Sebelius the message to the Clinton dead enders is this: Hey. Here's a qualified women who shares my philosophy. If you really think its Hillary or no one else then you are a bunch of hypocrites and I don't need you. Either get on board the train or not.
Is it a gamble? Yes. Right now the polls show that where Obama is under performing is with democrats (he is getting about 80% of the self-identified democrats in most of the polls I have seen, which is less than Kerry got). If he can bump that up to about 90% of self-identified democrats, he wins the election. Picking a women (even though it is not Hillary) would do two things: attempt to lure some of those dems back into the fold and, given who Sebelius is and her record, make a serious play for the rational wing of the republican party.
So, that's my guess. As to the timing: I would not be surprised if he did not announce until Saturday morning although I think the Obama campaign is open to announcing earlier, depending on the news cycle (for example, how much air time is the new - and most likely flawed - Zogby poll showing McCain with a lead for the first time going to get? If it gets too much, then maybe the VP announcement comes to get it out of the headlines.