The software is modular, meaning there are many "plugins" that the community develops to allow streaming from different websites that aren't built-in. Essentially, the "server" runs on your PC, downloads streams and transcodes them in real time. Your xbox 360 connects to the PC in "My Videos" and allows you to watch these streams on your TV. I have a fairly beefy PC, but I never see the CPU usage get above 5-10% so I don't think it's extremely resource intensive.
Out of the box, I'm able to watch YouTube, comedy central, major news channels etc. Plugins allow me to watch my Day 9 dailies on Ustream, as well as all the archives on blip.tv.
The whole thing took me about 20 minutes to set up, and then another 15 mins or so to set up some of the other plugins. It's extremely easy to set up.
Now I'm able to watch all my streams on my HD TV without having my PC hooked up to my TV! I've been using it now for a couple of days and have found very few limitations. I highly recommend it.
Hope others find this useful!