I don't have one, but I do remember reading reviews saying that they are pretty good coolers. Be careful about what other people report for temps though, remember that there are a lot of different factors coming into play. More important than what the actual temp is, is what the difference of cpu temp to case temp is - this is what defines how good a heatsink truly is. Also on that, motherboard temp reporting has never been any good - different bios versions can give temp readouts of up to 15C difference.
Anyway, the biggest concern I have with it is it weighs 780g. That's about double what AMD recommends for an athlon XP heatsink. You probably won't have any trouble with it, but I'd be wary of moving the case around too much without detaching the heatsink first (an annoying hassle, I'm sure). Basically I'd strongly suggest at least taking it off if you plan to put the case in your car to take to a lan - the last thing you want is to see that your heatsink ripping off your motherboard during a bump in the road. Or worse, your heatsink snapping your motherboard in half (unlikely I'm sure, but still a chance - this is why AMD and Intel have recommended maximums for heatsink weight).