On the whole these changes look pretty good. Thanks for the much friendlier wording the blog posts!
I'm a bit worried about the limitations in loading social graph data. It looks like large accounts will have to load significantly more slowly than before. The rate limitations on users/lookup also means caching will be more important that ever before for loading smaller accounts. Often users/lookup was the bottleneck in loading small accounts.
On the whole though, there are no show stoppers. The rate limiting on search is pretty exciting - making it per account based removes a lot of the uncertainty around per IP limits.
I do have one question at this point. In the Developer Rules of the Road it states "If your application will eventually need more than 1 million user tokens, or you expect your embedded Tweets and embedded timelines to exceed 10 million daily impressions, you will need to talk to us directly about your access to the Twitter API as you may be subject to additional terms." How do we do this - who should we contact? Is there any information available about the additional terms?