I've never used the 'hidden' function on OCnet, but have used it on other forums previously. I don't think it's necessarily for sneakers or lurkers. I just think some people don't like the idea of websites telling on them. It's kind of 'big brother-ish,' if you think about it. Who needs to know what forum you're in or what thread you're reading? FB is notoriously telling on its users. 'Like' a page or comment on someone's wall post or even drive from one city to another or attend an event, and FB tells everybody. I think maybe that sort of thing is starting to creep some people out. When you go to the library, do you announce to everyone, "Okay, I'm heading over into Art History, and then I'm going to check out some plumbing books in Home Improvement, and then I'm going to hit the Self Help section. I'll be back later to show you all the books I selected." Nobody does this.
I think those who choose to be 'hidden' in here just don't want their movements monitored and reported to everyone else that's online. It's a question of creepiness rather than subterfuge or deceit. They just want their privacy.