I am certainly no UI guru—my favorite UI is a Unix shell. But I think Comcast's DVR user interface is perhaps the worst UI ever; at least in the top (or would it be bottom?) 10. It seems like it's always doing exactly what I don't want. Nothing is intuitive. It gets in my way. It irritates me ever single day.
Here is an example of one of the Comcast DVR's idiotic UIs. I was recording The Bourne Supremacy when I decided to quickly change channels to see what was on the news. Instead of just changing the channel, it wasted my time with this idiotic question asking whether I wanted to stop the recording and change the channel or just change the channel. How dumb!? Just change the friggin' channel—that's what I told it to do in the first place. At least this time the destructive action wasn't the default.