Tried ID4 last night and everything worked fine in my combo player (which I was pleasantly surprised considering the problems it has with the most basic discs).

The popup trivia was cool and I liked how you could turn it on/off at will without stopping the movie.  I did find the font small and a little hard to read on my 50" TV.  I had to lean forward on the couch, but it could just be my eyes.  I realize it's a tough balance in trying to convey the information without obstructing the picture.  Perhaps a choice in font sizes would be neat.

The Index feature, while a nifty proof of concept, isn't very useful for a title like this.  I mean, why do I need to see every scene that has a "cigar" in it?  Though, as I mentioned earlier this would be really cool with something like the Planet Earth discs or really any kind of documentary type of show.  Or even maybe with more complicated types of movies (instead of a popcorn action flick).  Like, for LOST, what if they had a symbolism index or Lore index?  Then you could pick "Numbers" from the list and it will start playing every scene that references the numbers.  Or you could pick a particular number and see all those scenes.  Or pick "Jacob" and see every scene referencing him?  That probably made no sense to people who don't watch LOST.    Having an Index like this for the Lord Of The Ring movies I think would be pretty fantastic as well.