I built GNOME2 out of CVS for the first time the other day. I haven't played much with the gnome-core bits (in particular, the 2.0 panel kept crashing), but I've started looking at the part I really care about -- the development environment.
Mostly I've played with glib/gtk+, and the new versions are so much nicer than the old ones. I've always been fond of gtk+, but there always were some huge annoyances that made programming with it much more painful than was really necessary. I'm happy to report that the situation is now vastly improved... the APIs clean-ups are fabulous, and I'm loving the new tree and text widgets. Everything seems well-thought-out, which is about the highest compliment I can think of.
I love GObject. I didn't really realize how badly I needed interfaces -- now that I have them, I can think of a dozen places where they can really make a difference in my code.
I was worried that Pango was going to make things more complicated, but now I see how it makes everything so much easier, at least from the developers point-of-view. The fact that we haven't been able to do things as simple as mixing bold, italic and 'normal' text is totally idiotic. Now it is trivial, as it should be.
Now we just need to do something about the signal emission overhead...