The only major issue that I have felt in my use of Ubuntu till date(and to be fair, this is not ubuntu specific) is the problems I keep having with wireless setup. I can live with any of it’s other flaws. In earlier releases, the problem had been WPA support. The default install didn’t have wpa_supplicant, and to install wpa_supplicant, you needed to have network first, dammit! So I had to run around looking for a network cable, sit next to my AP, patiently download the package, figure out the unnecessarily verbose documentation and finally set up the stuff(in two terminals, one keeping an eye on the messages of wpa_cli).
Just upgraded my notebook to Gutsy a couple of days back. It is still in beta and would be released on 18th October. I recently changed my desktop over to Gnome from KDE. I have been a Kubuntu/KDE user for years, but the look and feel of KDE has remained tacky for a while now while Gnome had a very clean efficient look about it. But this also meant that I had the complete Gnome and KDE stack on my notebook, so I had to download about 1.