I just installed a Mandriva 2010 VM under VirtualBox, and to my big surprise, when it booted up, it was already "ware" of my Virtual Box environment. Things like grabbing (and releasing) the mouse and resizing the X11 window just worked right out of the box, no need to install the Virtual Box guest additions. Pretty impressive.
For some unknown reasons (I'm guessing someone trying to be overzealous about what the Fedora users should do), FC12 no longer includes the control panel to modify the "Window" behavior. This includes the must-have feature of "Select windows when the mouse moves over them". But wait, no need to switch to Ubuntu quite yet, there's a simple fix to restore this control panel:
$ sudo yum install control-center-extra
Unix is the next best thing since sliced bread. I've used it for a long time now (since 1985, on a PDP-11 running BSD 2.9). I prefer Linux these days, but honestly, I really don't care that much as long as it's some reasonable flavor of Unix.