The only car I've owned that qualified as a beater was the 95 Nissan Altima I traded in earlier this year. It didn't start out as a beater, but in the few short years I owned it, it completely fell apart (not through abuse either). By the time I got rid of it, it left a superfund site wherever I parked it.
Otherwise, I keep my cars for a long time, but I keep them in good tune mechanically and reasonably clean. I'm not as uptight about it as Daniel Flory, but I'm no slob either.
The 97 4Runner has roughly 135k on the odo, the 03 Camry has 85k. Barring any unforseen issues, I'll keep both till at least 200k, probably much longer in the case of the 4Runner (it's my hunting and camping vehicle).
The 95 Nissan? It had just over 100k when I traded it in this March. It had a bad oil leak, a bad water leak via the water pump, slipping transmission, dead airbag sensor, and rattled like crazy. The O2 sensor bung rusted out, so that was held in with jb weld. After redoing that twice in a year, the sensor died and I was left with a permanently on CEL. Any one of those problems would've been worth fixing, but the fact that all of them occured within 15k miles was a sign to me that the car was on it's way out.
Chris