On the main page, down at the bottom where you see "there are xxx users online...", you can click on that number, and it'll show you who's reading what threads.

And then add those bots that were mentioned and it gets crowded around here.
I didn't see them mentioned in this thread, but yeah. Most of the "guest" users you see are not actual people, they're search engine spiders, reading the threads. They do that so that when you, for example, Google "Ewaste", it knows what links to show you as results.