Most Helpful Guy
I use a pen name because I'd be too easy to locate using the phone directory.
(Just for fun, I once looked up an Aussie teacher I met on the internet and showed her a photo of her school. Those searches can be easy)
If I mention a vacation, burglars would know there's nobody at home at my address then.
I also got threats on other sites, as did other people.(one even got firebombed) And I don't want a girl (or a gay guy) ringing on my door either. :)
Several good reasons thus. Nothing paranoid, elementary precautions.2