I gave up on Ubuntu a while back - I disavowed the upgrades well before that. There remains one (netbook) Ubuntu in the house - on that I have disabled the upgrade notification. For just this reason. I re-install (clean) that machine usually 2-3 months after Ubuntu releases go GA - once the bugs have been ironed out.
One thing Ubuntu is good at is release co-existance. I always install to new partitions, and share the /home partition. This allows me to re-boot the old release simply by re-booting. The shared /home works fine. Well, it always has in the past - I've not bothered with Precise yet.
This works if you have a separate /home - or can create one prior to the install. In your case you could probably create the /home partition, then simply re-install the old release, specifying the /home mount during partitioning. Accept the same users/passwords, and you should be fine.
Note my sigline ...