I joined in November 2008, and this is my 150th post. That averages out to less than one post per day. At the same time, I may sometimes go two weeks without logging on, so I guess I do post on most visits.
I wouldn't say I've ever been a lurker, but I don't think I will ever catch up to the mega-posters here.
It is my experience, that on online forums and newsgroups, whether the subject matter is tickling or archaeology, the vast majority of members are lurkers, never posting even once.