If she does the full eight years as Secretary of State, the way she's doing it now, she'll have more relevant experience than most other candidates, the public will have had more time to forget about her less popular actions during Bill's presidency, and she'd have semi-incumbency advantage as long as Biden doesn't run as well. And there'll be still more desire then to have a female candidate, and she's the only real option on the Democratic side.

I think Snowe on the Republican ticket is rather less likely than Rodham Clinton on the Democratic one, really - and unfortunately. She'd be a formidable candidate in the general, but it does seem like a long shot for her to win the Republican primaries.