Admittedly(ashamedly) I've been caught up in a few commuter races. I am however determined not to do it again (well not much more). The fact is there are some days when I want to ride an easy pace and people shouldn't feel pride in passing me while I'm in a relaxed mode, and neither should I feel pride in passing somebody else for whatever reason. Though there are a couple situations that make it tempting. Like when somebody blasts by, and then slows down 20 or 30 yards in front of me, which tells me they probably went all out to pass me and are running out of gas, in which case I would actually have to slow down not to re-pass. Or if I pass someone while riding my normal pace and they speed up to pass me back. Nonetheless its best to refrain.