There was a company that built this a while back called Plura Processing. They got pretty decent distribution (50k-100k nodes at any given time), but even on flash gaming sites and such the user duration wasn't long enough on a pageview to get any real work done and report it back.

The press also took note of Digsby (one of their distribution partners) and the controversy was huge.

They are now out of business.

http://www.crunchbase.com/company/plura-processing

http://lifehacker.com/5336382/digsby-joins-the-dark-side-use...