A few interesting notes about heat and fan noise:
I watched several YouTube videos and iTunes movie trailers, all streaming 1080p or 720p over the Internet. The laptop got a bit warmer than when I installed Diablo III, but not hot enough for me to need to move the laptop off my lap. I wasn’t able to trigger the fans while doing this, and the videos ran smoothly.
I also used Handbrake to convert a movie file for my iPhone—the Retina MacBook Pro doesn’t have an optical drive and I didn’t try ripping a DVD or CD using an external drive. The file conversion took less than 5 minutes, during which time the fans did not run, and the laptop did not noticeably heat up.
It’s a bit odd that Roman Loyola notes the fans did not “trigger” or “run” during these test. I imagine the fans were always spinning but he did not notice any extra noise. Maybe these fancy new fans are indeed more quiet.