I recently tried GNOME 3.4 for about a month. I liked it right away: it's pretty and it's practical. I stopped using it because it slowed down my (old, granted) computer horribly after a few days (memory leak?). Restarting the computer made it feel faster again, but I like keeping the machine on all the time (I usually only restart when there's a kernel update in my distro). I went back to LXDE and my machine feels so much faster: even freshly started, before a few days of slowdown, GNOME 3.4 is slower than LXDE, and I use mostly the same programs on both: chromium, evince, gvim, empathy, totem, etc.