I use the Scrivener backup option to send zipped files to Dropbox. I have all my works on three separate computers as well.

Only thing I haven't covered is getting all my writing files backed up in the cloud. I find it irritating that Dropbox doesn't have a $5 pricing option. I didn't go with SugarSync because at the time I decided I thought I might be using a Linux-based netbook for awhile.