I was thinking along those lines with smart boxes and so on. Like you might not be able to narrow down the demos like you can with Nielsen but they probably could get some raw numbers from providers.
If cable companies are providing any more information other than subscribers by Zip where demo's are freely available they'd be in a shit load of trouble.
In other words, if cable companies like Comcast are providing advertisers info right down to the household level - I want to be first in line to sue.
Regardless, I wonder how valuable On Demand viewing is for advertisers. Most Comcast On Demand viewing permits people to skip over advertising. That could have change though since I last had Comcast. My new provider ATT's On Demand prevents you from skipping over advertising on most of their network programming On Demand shows.