It's worth it there for only having to leave your computer on and a program running, and you really don't even have to once you get a good buffer. I'd use newsgroups but I would have to pay for Usenet.
I don't really seed on Demonoid, though
edit: Public trackers aren't nearly as secure regardless of whether or not you're seeding. Why do you think stuff like PeerGuardian exists?
Gonna say yes of course but I had the same problem as Diunx described above when I used an account of a friend some time ago. For some reason seeding didn't work. Even the moderators on that site couldn't help me out 
Oh well I can try to figure it out eventually. PM me your email