In its latest study out today, Nielsen estimates that 2.5 million US households cannot receive digital television signals and so are without TV entirely.
You can debate the validity of that number, it does fly in the face of the relatively few calls to FCC call centers set up to receive calls about the analog shut off, but correct or not, I don't think there's any other numbers out there to compare it with.
What I find interesting are the stories that are beginning to pop up about how ratings have or have not been effected by the analog shut off.
I'm not sure you can draw any conclusions about ratings effects at this point because of the way Nielsen measures ratings.
Nielsen gathers its national ratings data from approximately 20,000 households equipped with people meters. While Nielsen does its best to mirror the US population demographically, it seems to me that simply being a Nielsen "family" implies a certain level of self selection.
If you have enough of a clue to manage being a Nielsen family, that implies to me that you're less likely to have been been caught by surprise by the analog shut off, and are more likely than average to be prepared.
The folks who got caught by the cut off are the least aware or the most procrastinating or disadvantaged in some other way that would likely keep them off people meters as well. So, I won't be drawing any conclusions about how the ratings have or haven't been effected by the shut off for awhile (maybe a long while), until there's a lot more information.