So Hilary Clinton has won Pennsylvania by what looks like about a 10% margin. She's still pretty much in line to lose the nomination unless there's a dramatic shift in momentum and she starts winning every state from here on out by 20% or more or the superdelegates decide en masse to throw in with the Clinton camp, but that's a plenty big margin of victory to justify staying in the race.
Certainly it's hard to argue that the momentum has shifted. Clinton is winning races and taking shots, Obama is starting to seem tired of the whole thing, and making sloppy mistakes that don't do him any good (like the "bitter" comments). He's also clearly the front-runner, and that's a much different position to run in. It seems like the Obama machine is having some trouble correcting for that new status quo.
As to whether or not Clinton *should* stay in the race, or drop out for the good of the party? Or whether Obama should, even though he's in the lead? At this point, they might as well fight it out to the convention. The damage has been done. A few months back, polls indicated that either candidate had a good lead (Obama had a bigger one) on presumptive Republican nominee John McCain. Now they're about even.
Now this isn't really all that telling, the polls aren't wholly accurate and even when they are, so much is in flux right now that it's impossible to get an accurate reading on what's going to happen in the general election. But it's hard to argue that this bitter fight between two rival candidates has *not* been a benefit to the Democratic party. It has instead given the Republican candidate a fighting chance in the next election.
This fact is going to only heighten the bitterness in the two camps, as each will blame the other candidate for dragging things out.
I don't really have any solutions to offer. I will say that the process has dragged me from "fired up, ready to go" to "Jesus, can we please have a fucking candidate already?" I mean, I'm still hoping to vote for Obama, hoping he'll be our President, but it's starting to feel more like naive optimism in the face of an increasingly bitter fight that looks pretty much like politics as usual.