All I really care about when it comes to the presidential election is that a Democrat wins. That has to happen.
I've been a Hillary supporter, but I could also be an Obama supporter. I just thought Hillary was better equipped to do battle with the Republicans and special interests "from day one" (as she says). I still think that. But if she's less electable than Obama, then I'll gladly accept Obama as the candidate. We can't have another Republican--especially McCain--get into office and continue the policies of George Bush. (I think McCain is talking the talk to mollify conservatives these days, but if he does get into office, he'll reassert his own slightly more measured principles. But that's not good enough.)
I still think that Democrats should elect their own candidate. Some of the primaries and caucuses are open to Republicans and independents. However, their votes shouldn't be considered in our choosing our Democratic candidate, especially in Red States where the vote will probably go to a Republican anyway. They might be an indicator (or not) of how the general election will go. That's speculative.
There is so much momentum and I dare say irrational fervor for Obama right now that one can speculate that lots of Republicans and independents will vote for Obama in the general election (more than for Hillary) and that with Obama as the Democratic candidate, the election will be decisive and not be at odds with the popular vote (i.e., the Electoral College won't matter).
I still think it's a little too soon to arrive at that conclusion.