Tone makes a big difference. Can't ever tell what people are saying, but I usually get whether they are friendly or angry. I don't think its inappropriate to speak to cyclists. Just choose the time and place wisely. After dark is not a good time (I consider myself a very independent woman, and am often out alone after dark. but the world does take on a sinister glow.) While moving is probably not productive (due to the communication difficulty). At a light... depends on how scary you look. Some people will always come across as creepy (usually men), and others as charming (or at the very least, non-threatening).

I enjoy comments, but only when I don't feel threatened in any way. Its an affirmation of biking, which can't be bad.