In the end, SuperDuper! and Crashplan came out on top as the bookends of a comprehensive plan: SuperDuper! for a full backup to an external drive, and Crashplan for off-site storage of mission-critical files. This is pretty much what I do, though I hadn't heard of Crashplan until I wrote this post!
The important thing here - and we know you've all heard this a million times - is this: Back up your stuff!