Viz Media has licensed the download rights for Death Note, an anime series which is very popular in Japan. It looks promising, though I haven't had a chance to view it yet. You can read their press release here.

A number of Japanese corporations have begun a fairly aggressive campaign recently to eliminate illegal downloads from sites like YouTube and BitTorrent. Therefore, I'm not at all surprised to see that they've started licensing pay-per-download rights -- I sort've figured that would step two.
In the next year or two, I expect to see a number of other TV series become available this way because it simply makes sense.

As long as the price point is reasonable and the quality is good, I expect downloads of this and other series will be a success. Apple has also recently come out with a nice little gadget, the Apple TV, for playing downloaded video on your TV, eliminated the need for a bit of geeky jury-rigging to accomplish the same thing with a PC. All the pieces are falling into place for downloaded TV episodes to become truly practical.