I do the same as Jo*mar.

For me Friday morning is back-up time - my Thunderbird, Firefox and Chrome profiles get saved to my two external HDs. Critical stuff gets backed-up on the fly.

Apart from that (external HDs have been known to fail...), I use CrashPlan (there are others) as cloud back-up; http://www.code42.com/crashplan/ .

For a few dollars a month it sits in the background, automatically backing everything up.