The Pomodoro Technique(TM) is essentially the same, but waltzing in 25/5 time. A longer interval makes more sense to me too, though. Maybe 45/15 or 50/10; either way, it helps block out distractions - "No, self, I committed to working on this for another fourteen minutes."

I wrote an Emacs work / rest timer (http://github.com/silentbicycle/zwiebel) for that sort of thing, if anybody's interested. (I hooked it up to an XOSD (http://ignavus.net/software.html)-based alert.)