I've got a Slash, I've run it but not raced it at South Lakes Model Car Club, here's a vid of it on our grass track:
http://uk.youtube.com/watch?v=ZmO8LIKTyKI
I'd like to race it stock if anyone else turned up with one. For me part of the appeal is leaving it stock, it's tough and handles nicely, but I think grip is it's enemy. The suspension is soft, so if there is too much grip it rolls too much, I wouldn't put better tyres on it because I think it handles nice when the grip is low. It's a nice balance compared to a typical 2WD buggy, it turns in really well, doesn't want to understeer like most buggies and if the back does step out it's really easy to get a nice power slide. Again too grippier surface (carpet / tarmac) spoils this though as it tends to roll rather than slide and cock and spin the inside wheel. It worked okay on grass as you can see in the vid, I tried it on a carpet track and the suspension was just too soft, I'd love to race it on dirt, but we don't have a dirt track. I've run it at a gravel BMX track, it was a lot of fun on the gravel, not enough power for huge jumps, but manages the small stuff nicely. As a low speed basher I really enjoy it, probably an excellent first time RC, if I got the chance I'd love to race it stock on a loose surface.