I know on BF you are supposed to pretend that you never notice other riders. But that is silly. Any man (or woman) worth his (or her) salt has a competitive streak. Also I have had some of my most enjoyable rides, dicing and trading pulls, with random strangers. If you have a plan for the ride, stick to it. If a little casual, impromptu competition is going to spice up your day, have at it.
Also, I have never had anyone react badly. The people who pass you and immediately blow up don't count. Other riders always seem to enjoy it as much as I do.