I have upgraded to WP 2.5 RC1 yesterday and noticed that there are some problems with tag clouds and categories. Have a look at the first post on my site and look at the 'Posted in' part. For some reason it's used the comments count as the category, when it should say 'travelogues'. The ink is correct, though. Then if you scroll down, you see that in the tag cloud some tags have been merged together.
Does anybody know what is going on?