I gave the app a whirl on my iPhone 4, choosing an episode of "Cowboy Bebop" from the TV listings. There's a sense of familiarity going, as I've already used the streaming functionality on the iPad, which was generally above average in performance and had respectable quality. The episode appears on my 3.5-inch screen, and after a few seconds the little algorithms adjust the quality of the image from '90s Real Player to "Ooh, Nice."
The app is available as a free download [App Store] to Comcast subscribers. No live tv yet, unfortunately. Other companies have tried to offer such services but have been met with legal issues with the licensing of the content.
Unfortunately it seems the early iTunes reviews shows some users having problems with crashing in the new version, so be sure to keep a backup of the previous version before upgrading.