I've had them since ~'99. The only difficulties i find with them are in lots of sticky sand. Keep them generously greased (the "mushroom" on the pedal and, in especially sticky sand, grease the (clean) cleats, too.

I've had good results in mud (except the goopiest crap in the DFW, TX area which will gum up any pedal... or even flat shoes!), snow and any other kind of stuff. With sand, if you let the lube on the pedal dry up, the engagement is hard.

I still wouldn't trade them for anything!