Per this thread and its solution, I'm using
compiz for enabling alt-tab window switch. It had been working as expected for a few days, but today suddenly it started to freeze the entire display. Since it stops responding with its keyboard & mouse, I have to login via ssh and reboot (I just wanted to be as nice as possible to the system). Any idea is appreciated.
Just describing my environment more precisely, I use this problematic Ubuntu (12.04,
Gnome Classic) machine from Mac via
synergy 1.3.6. And I particularly see this issue happen when I switch to
filezilla (FTP client). With
Gnome Classic (no effect) I've not seen this.