The Back button thing might drive me a little nuts. 14 years of muscle memory. Overall, it's "new but familiar." Some of the menus are designed poorly but if you know Tivo well, you can figure it out.I agree.
Yeah, I had to program the "Back" button into my Harmony (taking up the last unassigned button; hope I don't need to add anything else!), and now I have to untrain years of pressing left-arrow to return to the Now Playing list from a recording.
But overall, I'm getting used to it surprisingly (for me) fast.
I don't know how complete newbies are going to take it, though.