I'm curious about this. Especially when it is a new member whose first post is a response to a thread that has been dead for 5 years. I have this hypothesis that people stumble on a thread through google, and have such an urge to respond to it, that they register at the forum to do so. But 1) that seems like an awful lot of trouble and sometimes the replies are to rather mundane threads that don't seem all that inspiring. 2) they would have to go back an find the post the googled after they joined. That seems a bit too much trouble in itself, unless, I suppose they bookmarked it. Another idea, more implausible, is that an internet surfer discovers a forum like PF and says, "oh, physics! I love physics! And here's a whole forum devoted to physics! sayyyy... I bet they'd love to hear about my favorite baked potato toppings, or how I kicked my sunflower seed addiction. I'll join up and see if they have any threads on that!!" How do you think it happens? Should I survey necroposters and find out?