Some of them are search engine bots crawling and indexing the site, which is also a good thing. There's a mod/hack that can split them off into their own group, but I found it's not very reliable with some of the other stuff already implemented. And, yes, many of them are lurkers... so if you're reading this and haven't registered yet, please click here to join NSxB!

I'm sure part of it is because of people like me.  I'll get home from work late or something, and I just wanna see the new posts.  I forget to log in until I'm searching for a 'reply' button.  Sometimes i'm on the site an hour or more before I log-in because I don't find anything to reply to right away.