I've been using Virtualbox (now at 3.0.2) on Kubuntu (now at 9.04) for a while now, and I seem to have a problem when running Windows. Sometime after a while the audio will cut out in Kubuntu. The only way I can get it to recover is to make sure VirtualBox is completely shutdown and either going into multimedia under "system settings" and test the audio or restart.
I'm wondering if anyone else here has experienced similar issues and has come up with a more elegant solution. I can't seem to find a reasonable one at virtualbox.org.