This is sort of a Blu Ray question, or maybe just comment. Every Blu Ray I've played except one has run really well, really fast. Navigation and fast forwarding/rewinding has actually been faster than with most DVD players (or video rentals on the 360), which is pretty impressive given the massively higher computational power required...
...but I noticed with Mamma Mia, it didn't run nearly as well. I mean like fast forwarding and rewinding wasn't nearly as smooth as all the other Blu Rays I've played. My hypothesis is it's caused by a bulky Java interface overhead-like it's running some Java program that the movie runs on top of, or something along those lines. I kind of think that based on all the extra junk it has-I mean like you click pause and it pulls up this worthless movie specific interface that just duplicates buttons on your remote. You leave it paused long enough and it actually switches to a completely different video track playing the Universal logo.
It's kind of weird, pointless stuff like that. (Not to discourage anyone from that movie, it still runs fine, but...)
I also dislike that apparently I have to deny Profile 2.0 titles internet access every time I launch them. It's like no, I don't want this randomly connecting to the internet, there's no reason for that.
And my last random thought-what the heck is the point of VC-1 on Blu Ray (or HD-DVD before it)? My theory has always been that it's just some politics. Microsoft got it on there somehow or other. *I* can even tell the difference between it and H.264, and that's even on a 720p set. I'm not even 100% sure I like it as well as MPEG-2, given a high enough bit rate for the latter.
It just seems weird that they randomly include an inferior CODEC publishers can use, and that so many publishers use it.