[dnanian]

It's never fun or easy to roll back from an OS update. You can make a backup, retain that, install and then restore the backup to roll back, but then any changes you've made are a pain.

Sandboxes are a good way, and while you can Sandbox Lion from Snow Leopard, a lot has changed and who knows what Mail'll do if you're not using IMAP (for example)... so I don't recommend it.