There have been some people have tried "upgrading" from 11.10 to 11.04, mainly to get back the classic Gnome desktop. Please do not do this!!! There is a bug they will let you try to "downgrade" in place, but really all you will end up with is a non-functional Ubuntu System.
For more info please check out the bug report at:
T-V (not an admin, just play one on television)