LinkWorth is a system where you can sell and buy all kinds of ads and text links. I tried them for a couple of months and I would not recommend them to anyone else. First of all their system is quite complicated and you rarely actually sell something although you spend a lot of time to list your sites.
The worst part of the program was their affiliate system which didn't trace any single referral! And I had like 800+ targeted webmasters who followed my links so it's almost impossible that none of them actually signed up.