I'm not enough of a speed demon yet to get too involved in this... probably need to upgrade to a road bike before I do. Right now I'm on a relatively inexpensive hybrid with fully loaded panniers, and there's plenty of roadies out there on racing bikes I'm not going to compete with. Still, I get involved at times. If I see someone coming up behind me I usually speed up. If they are still bearing down fast I let it go without a wounded ego. The people I pass are obviously not too concerned with speed so it'd be downright silly to get competitive about it. Sometimes there are cyclists riding at a slightly slower pace and I might speed up to pass them, but it's not about being competitive so much as just getting the pass out of the way and making sure I can choose a safe moment to do it.