Is a 10.8 Time Machine backup restorable under 10.7
Yes, though there are caveats. I decide to try it and see; I reformatted my hard disk, installed Lion, then used Migration Assistant to restore the two user accounts. Until this point everything works perfectly, but there were two major unrelated problems to downgrading: 1) is a user account login bug with Lion that requires use of the passwordreset utility for the root account, and 2) Using Migration Assistant to migrate applications was a mistake, since many vital apps such as Safari and Mail won't work under Lion, and require many steps to reinstall properly.