I came across a fascinating interpretation/prediction on the Palin VP nomination in the comments section of a San Jose Mercury news article. Here's the theory (my version of it, anyway):

The Palin nomination has dulled the Obama/Biden momentum and media wave by sheer dint of its shock factor. McCain et al let the media chew awkwardly on it for a week, maybe two if the convention is muted by hurricanes. Then, Palin announces that she's realized the responsibilities of the campaign and VP post would do harm to her fragile Down Syndrome infant, that her first responsibility is to her family, that it's a great honor but that she must decline. Then, McCain selects a more suitable VP candidate, getting a poll bump as relieved supporters (and media) laud the now-departed honorable family values mom and heap praise on McCain's boring (but solid) replacement.

McCain upside:
1. Effectively flattened the Obama post-convention surge and media fawning.
2. Turned the heads of the mouth-breathing Christian right, filling them with positive sentiments about his being "on their side".
3. Gets a boost even with a mediocre VP selection after Palin, simply out of relief that this obvious minor-leaguer is out of the game.
4. Media is thrilled they didn't have to dance with the sharp knives on a helpless, daft hockey mom.
5. A few crazy women stay on the train just because McCain showed faith in a female candidate.

Downside:
1. Depending how it plays out, he appears rash/cynical/both.
2. If media gets after Palin scandals/incompetence quickly, it could appear she was forced out rather than choosing her family over the Vice Presidency. This would destroy the McCain campaign.

I guess maybe I'm paranoid, but I wouldn't be at all surprised to see it play out this way.