I think there was a thread along this lines a few moons ago, but I can't find it now.
I tend to find it the other way myself Russell, I end up having too much of a laugh and not really concentrating on the photos, but then again that depends on when/where. I got some shots I liked walking around Chester Zoo with Pete (Carr) we were having a laugh but we were both looking for shots and nicking each others ideas (well I was nicking his)....but then at focus (yesterday) I was too busy having a laugh to get any setting right, frame shots properly or anything really, not a great example as I didn't really go to Focus to get great shots, but it also happened at the last Blackpool meet, I got pretty much no decent shots, but had a good day out. I am guessing it is probably the mood I am in rather than who I am with. If I am out on my own it is usually because I am in the mood to take some photos so go out and do it. Meets are arranged in advance generally and I could be in any mood on the day.