Another board I'm register on allows someone log on to see who is online and who is viewing what. I do that regularly--not to see who is on line---but to see what is being viewed. It is a recipe type forum and most users aren't registered. I see then what recipes are being searched and are most popular. :) Extremely frequently, I see Google AdSense Spider, Google Spider and Yahoo! Slurp Spider that are 'bots' (software programs of a robotic nature I understand) that pulls unformation for their search engines. They are very efficient. As someone already mentioned, their search engines can often find posts for me (even my own!) that a forum's search function doesn't readily do. What is searchable is what can be had without logging in.
Something you might want to do is search in Google for your username. If stuff is coming up that you don't want seen I guess there is a way to notify Google that you want something (or anything searched with your username?) to be removed. I'm not up on this though. Someone else might be able to speak to this better.