If you don't have a site, don't want to list it for some reason, your site is down, etc. PLEASE DO NOT PUT SOMETHING LIKE "notupyet.com" or "dont.have.one" IN YOUR PROFILE. Instead just leave it blank or the default http://www.
I just find it so annoying when I view a profile to see a useless home page link. Nothing personal to anybody but a request in general.
Oh, maybe it's because since I actually own vB I can put something in there whereas some users who don't "own" it have to just fill it in with something although they still have a need to download mods for boards they don't "own" yet.