Here's the big changes that I have noticed with the new service upgrade(I'm using Friends as my example show) :
1. faster guide movement - used to be irritatingly slow
2. categorizing of recorded shows - multiple episodes of a show are now listed as "Friends (2)" when that show is selected it will then list the recorded shows - makes the "My Shows" menu less cluttered
3. Series recording - will record all shows of Friends and you can tell it how many to keep. It can also be told not to record repeats.
4. A recording history which shows the percentage of the hard drive used.
5. The ability to not record a previously recorded show. if Friends broadcast the same episode twice, and the first hadn't been deleted, it wouldn't record it again.
That's what I have been able to determine so far. I'm sure there is more, but these are the majors to me.