I think it'd probably be a good idea to add an option to set a minimum amount of time taken between backups.

This way if someone is going ham in the PopShop and installs a bunch of programs in a short period of time, it'll only make one backup for it. That way if one of them goes sideways and breaks a bunch of stuff (LTT Linus style) there will still be an update old enough to rollback too.

So if the min time is set to 15 min and it's only 7 min since the last package was installed/updated then it won't bother making another backup since the one from 7 min ago should be good enough.