Let the hive mind of Engadget get that for you.
"I am looking for a device that will stream sound from one source to several recipients. For example, I want to stream sound from my TV or stereo to my phone or MP3 player that has radio and Bluetooth capabilities. I have looked into radio transmitters and they seem like a decent choice, but I can't find one that uses external power (USB or from the plug) and I would want one with a transmit range of around 50 meters. Thanks!"
I agree. It was a useless feature on HD DVD and it will only be a marginal feature on Blu Ray. Not a single HD DVD justified hooking up the player to the internet and I think the same will be true for Blu Ray. Of course if you have a PS3 you may already be hooked up for other reasons but it will still be a struggle to persuade people to go online.
Most disks will ignore it entirely, or feature some crappy games with online scores, or bundle up a generic portal or store so you can download trailers or buy merchandise. Whoopee.
In theory, it could have *great* potential. Imagine that you got points with every purchase that you could redeem for downloads. e.g. 1000 points per registered disk. Maybe it could track your collection and even allow you to participate in buy 5 get one 1 free style deals. People would be rewarded for their purchases and for going online. You could use the points to download and watch TV shows, or perhaps even movies. Hell, a Blu Ray player could in theory even allow you to rent and download movies.
But for now and the forseeable future it is a waste of time. I doubt many people would even bother to hook up their sets to the internet. The feature has to overcome the meh factor and tossing people a few trailers, crappy games or things that should have been on the disk to start with is not going to do it.