I'll sign if I have a question about, comment on or am really blown away by their site. But this is rare. I just don't feel the need to sign everybody's guestbook, that's all.
I never do. I just don't take the time. I personally don't see the value in it - I figure that domeone else has already made whatever comment I would make, and I don't think anyone needs to know my name. Shhhhhh! Don't tell anyone my name.
:: wanders through the guestbook halls:: Dan? Hey, Dan? Da-aaan?
:: opens a random door on the left, peeks in:: Hey, any of you seen a guy named Dan? AKA Flatlander?
I usually sign the guestbook to let the person know I was there and to let them know what I think of the site. I usully email them about any specific questions.
I don't - just don't really see the value in leaving more tracks on the internet.
From the other side, on my different sites, I played with the idea of using them, but they ended up being another form of spam. Things would show up like "Like you site, come visit mine and buy...." So, I don't use them at all.
Not anymore. I think the time and purpose for guestbooks has passed - they were great when people were first starting up websites and such, but ... I don't bother with them anymore and plan to eliminate the one I have when I revamp our club's site.