Performance problem using Parallels - prl_vm_app always running at 100%

Gideon007 on the Fusion forum solved this one for me.
http://communities.vmware.com/post!reply.jspa?message=1991832

I had the a major performance problem with the prl_vm_app process pegging the cpu at 100% or more on my iMac using Mountain Lion (though I suspect this issue would affect other versions as well). The Windows Guest OS was not usable it was so slow.

Turns out deactivating the ethernet connection (which I had done earlier when switching it over to WiFi) was the culprit. After reactivating the ethernet connection, everything started to run in normal speed on the Windows VM instead of super slow motion.

This is a common problem to both Parallels and Fusion.

Hope this helps someone as I was going nuts trying to figure out the problem.