I upgraded to 2.0 this weekend, and I'm utterly disappointed in the user interface. The post entry function is taking a page from the MicroSoft book and trying to "be helpful". And in doing so, it's rendering the post in a way I do *not* want.
The worst symptom is rendering an "enter" (formerly a line break) as a paragraph break. I can't write two lines in a row, now. I do this quite frequently in my posts.
Additionally, using the "enter" key adds whitespace at the beginning of a line. I have no idea where this is coming from, but I'm forced to backspace in order to get rid of it.
This is the first upgrade from WP that has actually frustrated me. I don't want WP to "be helpful", I don't want it to "think for me"; I want it to do what it's told to do. I'm seriously considering downgrading to 1.5 if this is the way the 2.0 is going to behave.