What's in it for the advertisers?
I can speak here with some authority since part of my day job (marketing for a big healthcare company) is to oversee the online marketing programs for a number of our large brands. I haven't bought ad inventory on Revver largely because I work in a highly regulated industry and our target audience is going to far less interesting sites.
What I like, from an advertisers' perspective, is that I only pay for interaction. If we assume that the average click through is 3-4 percent, the advertiser is delivering "free impressions" to 97 people before he pays a dime. This works especially well for things like the Chapelle movie -- where there's a personality to the product that dovetails nicely off of viral videos.
We know that the timing of an ad is critical. You've reached someone that has just completed some entertainment and is likely to be in a more "open mood." More importantly, your ad creative doesn't have to work terribly hard to distract people. Unlike news sites or search engines, the people using Revver are not seeking. They're relaxing.
For the model to flourish, these clickers need to convert into customers. I don't know how that's going, but I hope it's going well.