Jonah Goldberg nails it:
I've been thinking about it and I think the bottom line on Palin is
pretty simple. If she does a good job at the convention and survives
about three weeks of serious media scrutiny — no horrible gaffes, no
unforgivable I-don't-knows to gotchya questions (fair and unfair), no
botched hostile interviews — she will emerge as the single most
inspired VP pick in modern memory and she will give the Democrats
migraines for a long time to come, assuming there are no terrible
skeletons we don't know about. But, if she screws up in the next three
weeks, gives the press and the late night comedians sufficient fodder
to Quayelize her, she'll be seen as anything from a liability to an
outright horrible pick. That's it. (more . . .)
Update: Ross Douthat's article "Palin and McCain's Judgment" puts him essentially on the same page as Goldberg. It's worth reading.