I played a match on Sunday. I normally have a reliable serve. I noticed the singles match taking place next to me and saw a guy consistantly foot faulting. He was our teams opponent and I thought about telling my teammate about it. I decided to let it go. Instead, I became concerned about my own footwork and began to double fault badly. I mean I was hitting a spin serve that was hitting before the net. I could not shake it. I agree with the original poster that once you call someone on foot faulting, you will destroy their service rhythm. Beware though that you could end up ruining your own!