I'm still working on getting this going for myself, but several people stream ota to their roku using their computer as a server. I plan on doing the same, and the investment is very small. The snag is encoding the video in real time - the only way to do it is to have a digital set top box and an external happauge hd box, otherwise there will be a delay - and of course only one channel at a time.
However, if you don't need to have real time, you can set up your computer to record the shows like a dvr, no resources being consumed, auto transcoded for you after the show is done (or late at night when you are asleep), and ready for you in a folder.
If you want free tv like abc, nbc, cbs, the roku is not the device to do that yet - a computer is with a tv card.
The problem is licensing and usage. The INDUSTRY is not there yet - has nothing to do with the roku. The reason is complicated, but eventually that business model will change as well, and you should think of the roku like a napster in that it is revolutionizing the way the content is being distributed - but napster is gone and now we have itunes. Roku may stick in the long run, it may not - but for the price point and the quality, it is a great start.
As for the news, or late night shows, there are private channels that have great content, as far as I am concerned, and the short lengths to me is a plus - I'd rather have a sampling of lots of things than one show to sit through.