“Desktop Effects” (aka compiz) is nice but it reduces the number of virtual desktops to 4. Come on, who can work in just 4 desktops!!?!
I finally worked out there is a way to increase this, although it’s completely non-obvious and not exposed through GNOME (bug 382901).
# yum install ccsm
Run ccsm (CompizConfig Settings Manager) which has the strangest most non-intuitive interface since Blender. Go to General → General Options. Go to the Desktop Size tab. Change Horizontal Virtual Size from 4 to the number of desktops desired.
That’s it. Not clear if you need to save that setting, but I guess I’ll find out when I next log in.