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Also, it does indeed look like Compiz works under 3.0: Just make sure you install the Linux guest additions, then you'll be able to turn it on under appearance.
Note to anyone else that wants to give it a try: I think the Kubuntu derivative is much more "flashy". The main Ubuntu distro is made to be simple and easy to use, so it uses the Gnome desktop. Kubuntu defaults to using the KDE desktop - which has a billion more options (and could be confusing...