Actually, the Roku is kind of lame. I know, I have five of them
We mostly watch broadcast television -- live or time shifted (we also have five DTVPal DVRs). When we are using the Roku, it's generally to watch Netflix -- which is available on just about any device.
We have some videos encoded on a PC and server them up with Plex or Playon and watch Food Network, History Channel, and Hulu on Playon.
Streaming media falls down on two counts: 1) you cannot turn on the TV, watch stuff, fall asleep, wake up, and still be watching stuff, and 2) there is no local programming -- I cannot see how my teams did or what the weather will be tomorrow.
Aereo addresses both problems. It's coming to my market next month and I'm going to sample it. Aereo is supposed to stream 28 channels to my Roku and provide DVR functionality. If that works out, a lot of people will be cutting the cable.