I'm using FC2, usually with Gnome as desktop. Sometimes I switch to KDE by using switchdesk. After I used the graphical version of switchdesk (switchdesk-gui) to switch to KDE, I am unable to set Gnome as my default desktop, no matter whether I type switchdesk GNOME or use switchdesk-gui, the default desktop remains KDE... The only way to start Gnome is to select it manually from the graphical login window.

The .Xclients-default file refers to GNOME and /etc/sysconfig/desktop contains DESKTOP="GNOME". Still the real default is KDE. Is there anything other setting that determines the default desktop?

Remove the .Xclients and .Xclients-default file in your user home directory and rerun switchdesk. I know it's a kludge but that is the only way I can get it to work for me. Looks like there are a few bugzilla tickets concerning this issue.