Internet TV viewing, especially that based on subscription, still hasn't quite taken off. The limited availability and newness of the technology, along with the newness of the readily available bandwidth for it, have all led to a very slow adoption. That's expected to change, however, and the number of people using IPTV is expected to nearly double every year for the next four years. That gives a rough estimate of over 40 million subscribers by the start of 2010, nothing to shrug at and definitely something the traditional TV providers will notice:

"The fight to capture the expanding base of IPTV subscribers will put telecom operators on a collision course with existing pay-TV market competitors and with a new class of broadband video portals as they roll-out progressively more sophisticated offerings," Mark Kirstein, vice president, multimedia content and services for iSuppli, said in a statement.
IPTV can offer quite a bit more than existing TV, such as more interactive or easier on-demand content, so we can probably expect the pay-TV providers to retaliate soon. Hopefully they retaliate with innovation and better products, instead of litigation.