The concept is pretty straight forward, good content sites bringing in eyeballs and only the really interested ones click thru to your site. Kinda like having an overture ad but filtering out the tire kickers. You only pay for the viewers that are more qualified & get to your site.
I was reading up on them recently because they contacted a client. A few years ago, they got slammed on another board for trying to sell traffic by the click. Can you imagine pay per click traffic? That's outrageous! That was before Overture & Adwords made PPC an accepted method.
I know 2 members here that are with TL. Both are pretty bright fellows.