I don't usually register at forums. In fact, I never even browsed forums until one day while downloading Naruto from Gotwoot's main page I accidentally clicked the forum button. The topic title in the Naruto discussion section caught my eye, so I clicked on it and started reading. Ten minutes later, after reading most of the current topics, I registered, and made my first post. I was the most noobish of noobs, completely ignorant of everything forum-related. We didn't even have rules at that point to refer to. And, Terra mistook me for a guy, but then, I thought he was a girl. Understandable, I guess, since I had my Shikamaru avatar that I'd made in Paint 5 minutes after I joined.
Subsequent forums I've joined up at have been only when I was about to make a post. Generally though, I won't lurk at a forum. I'm either signed up there and active, or I never browse it at all.