WordPress v2.0 Beta 1 was made available late last week and by the looks of the activity over on the special beta forum a lot of people are giving it a good test!
There is a growing list of plugins which have been tested with the beta for compatibility which can be found on the codex and everyone is welcome to contribute. I for one have to work on my version checker plugin to make it WordPress v2.0 compatible as the current css leaves it overlapping the main logout and profile links.