I'm in the waving-to-other-cyclists camp and most around here wave back, even if it's just a finger slightly raised off of the bars. The thing that bugs me, probably too much so, is when someone passes me without saying anything. I mean, it's common courtesy for a quick "on yer left" or some such or maybe even "Good morning!" This happened on yesterday's ride, actually, and I semi-shouted "good morning to you, too!" as the racer boy sped away.