I’ve just upgraded to WordPress version 2.5.1 with no problems what so ever which is expected because the 2.5.1 fixed bugs and a major security hole.
There is one thing i noticed is the fact that the backend is a little quicker and more responsive and they have fixed the uploader problem that i posted a week or two ago. The best thing about the new WordPress version is that new automatic plugin upgrade, it works like a treat if you run multiple blogs.