I'm using Windows XP via rdesktop 1.6.0-2ubuntu2 on Ubuntu Karmic, using the default compiz/GNOME combo.
I've got an Nvidia card with two displays attached. I've got Xinerama disabled, so I've got two subdisplays (:0.0 and :0.1) ..
I do my main work on :0.0 on linux, and have the Windows XP running fullscreen (-f) on :0.1.
When I've been working in XP move the mouse to the Linux screen, clicking into (e.g.) a GNOME terminal window, the focus doesn't move over, and the keyboard events keep showing up in XP. clicking the terminal task in the task bar or otherwise switching applications using the mouse fixes the problem - just giving the window focus doesn't. I can work, but it's annoying.
P.S: I'd be using Xinerama if artifact 1492062 was fixed ...