Just don't use unity
the solution to the above issues is quiet simple: just don't use unity!
It has nothing to do with X.org version. Parallels Desktop 6 works fine with the current X.org. (BTW that's why I upgraded my Parallels Desktop for Mac from Version 5 to 6.)
If you have already running a working Maverick (Ubuntu 10.10) here is how to upgrade to 11.04:
Start the Ubuntu upgrade. When it finishes, don't reboot! Remove Parallels Tools completely from your VM. (I did an update-grub, just in case. Don't know if it is necessary or not here, it helped in the past.)
Reboot into the new kernel. There will be message box that your system (due to missing 3D support) will not be able to use unity and you should use Ubuntu classic as your default session. (Due to missing 3D support it will start Ubuntu classic anyway without your action. But beware after reinstalling Parallels Tools this will not be the case!)
After successfully being logged in. Change the configuration of the login screen to use Ubuntu classic as default (actually I prefer Ubuntu classic without effects). Make sure you have auto login disabled. Otherwise you might run into unity if it is still the default.
That's all enjoy your Ubuntu with the Gnome Desktop as you ever did. Forget about this Unity. Although I use it on my Samsung NC10 Netbook quite successfully, it is a "nice to have" on a Desktop with an 24 inch screen.
If you wonder why Parallels did not support Unity, just think if you would do spending lot of work for a niche product, today nobody can tell if it will be accepted by the community.
Instead give reply to Ubuntu not to remove Gnome completely but still leave it as an option. Further to add more freedom of choice for the users to choose the desktop manager by them self, instead of just changing things which might not work on all platforms properly.
Cheers,
Andreas
P.S.: you don't have to do without any 3D support you just have to do without unity! 3D in Gnome works still fine.