The weirdest part, for me, was the way Palin kept on insisting that she was explaining in full her reasons for stepping down, and being deeply honest with the wonderful people of the great state of Alaska. But in fact, despite the ungodly length of the announcement, she offered no remotely satisfactory reasons or explanation at all (okay, there was some mixed-up stuff about keeping your eye on the basket without looking down at the ball, that then slid into some other mixed-up stuff about how, actually, the important thing is to keep your eye on the ball, but I'm pretty sure in sane-people-land none of that counts). There's no substitute for watching the video itself in full, but my favorite summary so far is Gail Collins:
Basically, the point was that Palin is quitting as governor because she’s not a quitter. Or a deceased salmon.
I have no clue why Palin did this, but I feel extremely dubious toward anyone trying to spin it as some kind of shrewd or "brilliant" political chess move. Who can watch that mess of a rambling speech and honestly think it was given as part of a crafty-genius master plan? It strains credibility for folks like Mary Matalin to even try to pretend they see the method behind the madness here.
Best observation I've seen so far on the "why" front comes from hilzoy, who has this to say:
Nothing I know about Sarah Palin leads me to believe that she would give up power voluntarily, let alone for something that is such a long shot, and in such a transparently self-destructive way.
I think that's a smart psychological read on Palin, so while we wait for more substantive info, I'm putting myself in hilzoy's speculative camp: "there's something we don't know about." Looking forward to the return of 24-7 Palin coverage while we try to figure out what it is.