Damn, Roy beat me to this one! *curses*
If you ask me, it's a heck of a gamble by Clinton... perhaps the only move she has left, but nonetheless a risky one. Anyone who's ever watched, say, The O'Reilly Factor knows that head-to-head, unmoderated "debates" degrade into shouting matches at least 90% of the time. In such an argument where no point can be adequately made, the only things that matter are appearances and charisma... and which candidate has the edge there?
Still, it puts pressure on Obama. If he accepts the challenge, he gambles pretty much everything on a good performance. If he declines, he gives Clinton ammunition to use against him. Either way, his image will probably be tarnished - even a good debate will allow plenty of chances for bashing and such. I think Clinton should have done this earlier if at all, but it's an intriguing development.
As for the "as long as he doesn't lose by 10% he's fine" thing, fp... well, I'm a little curious if you meant to give Clinton's exact margin of victory in Pennsylvania. ^_^;;