Boot from sandbox or just use it as a backup.

[dnanian]

No, if there's nothing wrong with the drive, there's no need to reformat. Just use Smart Update, and we'll put things back where they should be.

Migration Assistant would bring over your applications and the like, which you'd probably want. And it's a lot easier than dragging things over (since you wouldn't be able to be logged in when dragging things over, etc).