A friend of mine runs clips and has done a triathalon. She is used to the faster-paced stuff. We went together through a lot of very technical trails (average speed probably 4-8mph--on my 29er I am usually on the 32t front and largest two gears in the rear) with lots of bumps and rocks and roots and branches hanging everywhere, and she was having a lot of trouble. I am far more used to that kind of riding where one's ability to manipulate the bike is IMO a larger factor, and I still have to put my foot down 5-10 times on aggressive days (and that's just a one-hour run, heh). There are probably occasions where I put a foot down that being clipped in would have either made me approach more cautiously (and not needed to put a foot down), or where having my feet firmly attached to the bike would have allowed me to get through whatever obstacle caused me to put the foot down. Still, I am confident I would have gone down at least a few times so far (she did at one point, just a fall over).

I am better than average, and at least for my preferred style of riding (relatively slow and quite technical), I think clipping in would do me just as much harm as good.

So, at least until I get into faster-paced riding as opposed to slower, more technical stuff