So, call me cynical (I have been called much worse), but my immediate reaction is to wonder whether I should upgrade--what Twitter has done to make it a worse experience for me to use. That seems to be the overarching MO for stuff like this. I mean, I'm using Twitteriffic right now anyway, but still, I'm sure I'm not the only one wondering if they've hosed yet another of their first-party apps, and that can't be a good thing.
(EDIT: All that said, I just downloaded the Twitter update just out of curiosity, and it's actually pretty nice! I haven't yet seen any regressions from the previous version. And I haven't seen any sponsored tweet crap, but it's only been a few minutes.)