Nothing contrary to what you'd expect out of disc playback—it's just the same old DVD functions when you boil it down—but one cool feature is that the Blu-ray Title Menu is accessible while a movie is playing. Very convenient that you don't have to quit the movie to change language options. This is more of a Blu-ray feature than a PS3 feature, but it's nice that it's there.
All in all, Blu-ray playback was pretty great over HDMI (component should be fine too, but we don't have any component cables). There were no skips and everything played back perfectly. For all the trouble that Blu-ray has caused Sony, they actually managed to get playback pretty much on target.