Aren't they a "marketing" insurgent?
While I understand the opportunity to generate revenue that could be used to offset costs and keep prices from increasing, doesn't this compromise the site's ability to offer their own ads? What if an injected ad accidentally covers an ad sent by the original site? If that happens, where is the advertiser's recourse? The site sent the ad and from their perspective, the ad was viewed, they want to be paid.
I suppose it's no harm done if it only costs the advertiser when the customer clicks on their ad but I suspect site owners are also compensated by advertisers for page views.
If this becomes rampant, will sites switch to SSL (HTTPS)? Unless there's an agreement between the ISP and the site owner, justice would be served if most sites went SSL thereby making the appliance just another technology "door stop". Depending on how quickly sites followed suit, it would also represent an almost "overnight" end to whatever revenue was being generated. I wonder if Mediacom thought about how quickly the ROI on their appliance could end up a big fat zero?