I have just upgraded from Parallels 4.0 to 5.0.
It was an excellent upgrade and very easy.
Ubuntu/Kubuntu 9.10 is totally supported in 5.0 and I was able to intsall/upgrade Parallels Tools in 9.10 completely.
I had 9.04 installed and then used the Kubuntu upgrade to upgrade to 9.10.
I had three problems which resolved themselves upon restarting the 9.10 VM.
1) My mouse cursor dissappeared completely. It was recognized by Kubuntu, but was not visible. After restarting the VM it came back
2) The screen resolution dropped to a lower resolution. Upon restarting the VM I was able to re-establish the 1900x1200 resolution I had under 9.04.
3) The sound was coming through the "internal" speakers not the "line-out". Again, after restarting the VM, all was good.
I don't know all the feature upgrades of Parallels 5.0, but I am exploring them. Another nice thing, however was that my Windows 7.0 VM ran smoother.
If you are hung on getting 9.10, I would suggest upgrading to Parallels 5.0
Stephen McConnell