Shockwave.com is dynamically pumping advertisements into game content, as opposed to preceeding games with unrelated ads (which they also do.)
Unfortunately, the system appears to be focused on slapping ads into virtual billboards and whatnot. Ads are more effective when thoughtfully integrated into games. For example, Burton gear in a snowboarding game. Or players on the sideline of a sports game, drinking virtual Gatorade.
Perhaps this degree of sophistication isn’t cost effective in a casual game network. Then again, given the dramatic (and demonstrable) benefits of careful product placement, perhaps not.