CBS plans to run as many ads as viewers will tolerate, and if that sounds like what happens with regular television advertising, it's because it is! Hulu, on the other hand, wants to run fewer commercials but charge at least twice as much for them. On the TV side, FOX tried something similar last season with "Remote Free" viewing during Fringe and Dollhouse, where there were fewer commercials, but unfortunately FOX was not able to sell the remaining ads at premiums that offset having fewer commercials. Will Hulu be able to?
Business Week has an article that goes more in-depth about the contrast between CBS and Hulu.