i am usually wary about upgrading to a new major version of a software program. any software program. in wordpress 2.5, which was released 29th march, my view has not changed. i have become naturally paranoid (thanks, in part, to microsoft) of any major software updates — current plugins may not work or the modified theme may get messed up a bit.
so when version 2.5.1 came out last april 25 i knew it was time to upgrade the test blogs and eventually the rest of the bunch.
but before taking the plunge, make sure that you visit the wp forums often to see what problems other people have encountered and if there are solutions for it. forewarned. forearmed.