Everyone in the blogosphere has done one, so here's mine.
I'm with Schaller, but I'm going to add an argument that I think he missed: running for President is goddamn hard work. If you're serious about it, you have to start six months to a year before the Iowa caucuses, and then you have to spend pretty much all your time campaigning. Long, long before a single ballot is cast, you will have endured endless rubber chicken dinners in Iowa and winter festivals in New Hampshire and eight-hour marathon fundraising sessions on the telephone, shaking down donors for cash.
A modern presidential candidate needs at least a couple of the following: an awesome work ethic, great self-discipline, intense motivation, a huge war chest, and/or a really great primary staff. Obama scored high on the first two and the last. McCain had the motivation part down -- I'm no fan of McCain, but you had to give him props for sheer relentless stubborn doggedness. Going back a couple of cycles, Bush and Kerry both scored high on the war chests, and both had staffs that were good-to-excellent through the primary season. (In the general, less so, but we're talking primaries here.)
Palin could easily assemble a large war chest... but that's about it. I'm not seeing any of the character stuff, and her staff... well, at the moment she doesn't have any, really. Which is IMO suggestive right there; if you're going to run, you need your Plouffes or Axelrods lined up well in advance.
Anyway. Running for President is a fantastically tedious process, and there's no easy way around that. Attempts to short-circuit it have failed spectacularly. Skipping Iowa doesn't work (Giuliani). Coming in late doesn't work (Fred Thompson). Staying above the fray with a "big ideas" campaign doesn't work (Bill Bradley -- remember him?).
Related to this is the fact that Iowa and New Hampshire primary voters are spoiled rotten. They expect to see the candidate in their state again and again over months, sitting in diners having breakfast, shaking hands at the state fair tractor pull. History suggests that they are exquisitely sensitive to the slightest hint of distraction or inattention, and will punish it mercilessly. Not once have Iowa voters given the palm to a late-comer: the caucus has only ever been won by candidates who announced well in advance and then campaigned relentlessly.
So, I'm guessing that Palin will either (1) do the smart thing and not run, or (2) try to pull a Fred Thompson, announce late, not campaign much, draw lots of crowds, raise a lot of money, and then get beaten like a red-headed stepchild in both Iowa and New Hampshire.
And that's about all I want to say on the topic of Sarah Palin. Well, other than that this article on her travel by private jet is pretty cool. Someone went to the trouble of checking the flight logs: that's actual, you know, journalism. Good for Joe McGinnis, or for whatever nameless intern he's got running after this stuff.