I'd prefer this didn't happen. An anonymous visitor may just be a regular accessing the site from a different machine, or one who's just purged his cookies. I don't want to suddenly find myself looking at a completely different layout just because I happen to be logged out, or to have no idea what a non-member is talking about when they describe a front page I will hardly ever see. At present the only difference in appearance between logged in and not is a few details such as my name at the top right and the voting buttons. That's how I'd prefer it remain.