Another interesting feature that I've stumbled on is if I'm watching, for example, a particular channel during my lunch on my PC browser, if I tune to that channel later that evening on my Roku, I can go back by rewinding within the program that's currently on. I don't know how far back it goes, I've only gone back to the beginning of that particular program. I haven't tested to see if the same thing would happen with the channel I had on the night before when I stop watching. Note, I am not hitting the pause button or recording that program that I can rewind to the beginning in the evening.
I've also noticed that sometimes I can go back within a live program when I'm going back and forth between different channels, watching programs I'm not currently recording. This happened last night while I was watching some college football games. I had missed a play by switching to the World Series, and then when I went back to the college football game, again that I wasn't recording, I was able to rewind to see the play I'd missed.