Some of the anonymous people are actually registered people. If you stay logged on but aren't actively roaming around the site, after 15 minutes you get bumped down to anonymous status. So if the last page you were looking at before the phone rang, or your kid screamed for your attention, or the cat yacked up their dinner and you need to clean it up, was the "who's online" page, that's where the anonymous person's presence will show up. If you'll look closer, sometimes it's "my home" that they're at, so it's got to be a member.