I have mentioned PlayOn before, as the way that we are getting a lot of our television content. We use PlayOn to view content from Hulu and SyFy channel. Since PlayOn is a UPnP server , we are able to play this content on our Xbox or on our Media Center PC.
It looks like Roku is getting access to PlayOn content. The addition of the content that Roku already had, the addition of PlayOn, makes Roku a credible solution for cancelling cable or satellite service.
I am not sure if once you set the Roku up to access PlayOn content, if you need to leave the PC running to access the content.