One of my many failings is an obsession with backing up data. I'd like to say this is a result of my growing up with data storage devices like cassette tapes that scarred me with a lifelong mistrust for all backups. However when you come down to it, I'm just a little bit crazy. Anyway, one of my backup regimens includes copying all of my essential documents onto an 8 gig encrypted thumb drive once a month. The best application for this job is ChronoSync. I bought my ChronoSync license years ago and was really pleased this week to find out that: a) they released a new version 4 with several significant upgrades; and, b) ChronoSync developer, Econ Technologies, does not charge for upgrades, ever.
If you want to sync two folders or make sure a limited portion of your "stuff" gets copied to some other place, take a look at ChronoSync. I've been using it a long time and never had a problem.