It appears that CBS released a high definition player yesterday at the CBS labs area of their website. In addition, they realeased a few HD clips that are streaming in H.264 with the best resolution currently at 720p. However, according to techcrunch, CBS plans to support 1080p very soon.
At techcrunch, they provide a nice analysis of this in comparison to Hulu's HD quality offerings. here is an excerpt:
"Hulu currently provides three levels of quality: 360p, 480p, and 720p. The first two levels are streamed whereas the third is progressively downloaded. Since CBS has yet to stream anything above 480p, these new tests are nothing extraordinary…yet. However, even if CBS begins to stream 720p or higher, consumers might not see much benefit. According to Feng, the median broadband download rate in the US is 1.9mb/sec and high definition video (ordinarily considered 720p or higher on the web) consumes 2.5mb/sec. So if CBS tries streaming 720p, they'd probably run into lots of buffering issues."