My "I don't know if I will" is mostly because I'm not the regular DM of my group, I'd much rather play 3.5 than not play at all or look for a new group, and I don't know what everyone's reaction to the final version of 4e will be.
My guess is that we'll probably switch in the first campaign that starts after 4e. I may run Keep on the Shadowfell as a 1-shot test case, or join a 4e PBP game before that. But it's certainly possible that there will be things that are deal-breakers for me and the rest of my group. I don't think there will be; even if we have just as many (different) gripes with 4e than we did with 3.5, we'd probably flip just to keep current. And I've got a lot of hope for mechanics moving in a direction I like.