I just keep everything I care about in my Dropbox. I use enough machines on a day-to-day basis that this leaves me with a decent local redundancy, and having it all on Dropbox means that I'll have access to it even if all of my machines go down at once.
I fear Dropbox may be more like RAID than like backup: what happens when a file is deleted, causing it to be removed from all of your redundant machines?