I've been wondering, why hardy's repositories didn't include gimp 2.5.0. You should think that such an important software package would be updated quite fast, but maybe i'm missing something.. Luckily, I found a detailed instruction on how to build gimp 2.5.0 on ubuntu hardy. The nice thing: it worked.

Well, actually there was one package missing, which was easy to install via

Now, i'd have to see, if it's worth it.. I hear, they're working on gimp 2.6 and to have a look at some of the ideas contributing to the gimp interface, jump over to Gimp UI brainstorm.