Although it's a technical requirement in the current implementation of #newtwitter for the back button & crawling to work, I think part of the attraction of twitter was having your own simple URL. Now http://twitter.com/ev becomes http://twitter.com/#!/ev, which I can imagine confusing non-technical users.
It still works, but now you have two URLs for one resource, and when you go to the original URL it redirects you to the #! path, which judging from my timeline, people notice.
