Q: How can I downgrade from Mavericks to Lion 10.8?

If you have a bootable backup, you can do it - but you have to boot from another source, wipe your hard drive completely and then reinstall.

Unfortunately, it is not - you can restore from it once booted into an OS, but not initially boot from it (as far as I know). The problem in this case is that in order to downgrade, the drive needs to be wiped which means that it will also delete the recovery partition and you cannot install an earlier OS on top of the current one. Here is some TM info (read the TM vs. Clones in particular):

http://pondini.org/OSX/Home.html