I have a set of singletracks - also no experience with mammoths.
I've been using them for about with no issues for about 1000 miles. They've taken some pretty good hits and aren't out of true a bit - had them in the truing stand a week ago checking them. Made a couple of adjustments, but still within 1mm of true and round.
Great rims with a really crappy build (not tensioned properly, etc) won't last long. A well-built wheelset will last awhile unless something really bad happens, but few wheelsets will survive the really bad stuff.