I have found them in my queue too, if I run a whois and browse. Often, if I do queue for one of their files, I get a start if I give a start, likely cos they are using Moni, but theres plenty that dont...
Worse are the people with 100 slots open, and a fair few active downloaders, say, 40 or more, their available bandwidth is being shared by so many, the download only runs at a crawl, often less than 0.05kb. 0 of 0 users actually give a better completion rate!
Then, if I do find myself in the queue of a 0 of 0 user, I just right-click and select 'Find Sources Now' and waddaya know...