I try to keep my lappy as "clean" as possible and really don't STORE pics, music or scrap stuff on it at all. I have the room to, but just don't... b/c it seems like once I get into that habit, I get lazy with backing up (NOT good - I've learned the hard way on that!!)
I upload all of my photos and LOs to SmugMug, which keeps the original size/version, plus I backup to DVD four times/year, backup daily to Mozy.com (which is automatic, so I don't have to actively do anything), and backup oncee/month to my EHD.
I don't really consider my EHD a form of reliable backup, but I do consider Mozy, my DVDs and Mozy to be a backup.