I've been looking into some paid link systems, signed up for a few and never did anything further.
One company, Pay per Post (don't want to give them a link because so far they don't deserve it), gave me some free credit to try out their system.
I set up an advertiser account, and posted an opportunity... and over a day later it' still pending. From what I understand reading their forums most of the bloggers or posties as they call them, aren't very happy... even though they seem to be more important to pay per post than the people spending the money.
I'll likely do a more thorough analysis of the success of pay per post at a later date.
Maybe they'll even earn a link.