Just updated to WordPress 2.5 one of the easiest updates I’ve done (though NowReading doesn’t seem to be working properly. The new dashboard is good; though there are a few issues that others have mentioned that I’d agree with (e.g. the categories now being at the bottom of the posting area, where you may well miss them – given that the publish button is to the left.
I’ve just noted, though, that the categories can be sorted by “Most Used”, and on my screen the 5 that I can see are likely to be those I’ll be using.
Aaron Brazell has got some other points about it; overall, though, I’d say it’s an improvement.