Yeah, it does get a bit discouraging when people do not reply to your thread. Namely if you are somewhat new or not as popular within the forum community. Sometimes I'll stalk discussions or reply to a topic, but it's really all about what I wish to add on. If I have nothing to say, I have nothing to say. Or if I don't exactly know how to respond to a topic, I'll simply spectate at the side.
In the help threads, as Phatom said, I'm helpful only when I know what I'm doing and talking about. If it's something I'm not too familiar with, I'll allow a more experienced member to help the person in need of assistance. The last thing I want to do is steer someone the wrong the way, lol.