The main reason I keep coming back to OVP more than nearly any other forum on PC is because the discussion points are, for the most part, very laid-back and easy to contribute to. For me, 'good' OVP threads are ones that are broad enough to get really simple, often one-line answers, but also really deep and thoughtful treatises on the topic at hand. I like to post answers that are probably in-between the two, but I often like reading people's responses, so a mix is always good.
In terms of how many I respond to: in all honesty, unless I can't think of a single thing to say in a given topic (or if I have a feeling that it'll be closed for whatever reason), I'll normally respond to every thread made. When I spend time away from OVP, I have a tendency to binge on topics when I come back. A few days ago, for example, I posted in 40! That was kinda cool, but it has led to some people saying I've 'raped' OVP before which - while not conjuring up the best imagery - is something I can understand and sympathise with.