I upgraded to X.org, kde3.4 and Gnome2.10 all at the same time and all I had were a couple of problems, a problem with running root programs in kde, which I also had in my old version of kde and which is now fixed and the problem with kppp , which does work as long as I don't set it to dock into panel. And as I also mentioned, it is too slow to start up in gnome and xfce4 so I wanted to try a different dialler anyway.
Upgrading gnome also fixed about half a dozen niggling little problems that refused to go away in both 2.6 and 2.8 so I sticking to something that works doesn't really apply.
I don't really see the point of never upgrading something just because it might not work.
I'm a beginner, I don't have anything of critical importance on my computer so I don't have much to lose by trying different things.