I think there are many flavours within this concept, and I would actually think the majority of them would be legal.

If the concept works within the scope of devices passing links to favourite contents between each other, I don't see anything illegal with that. (And given use cases where two persons quickly pass each other on the street, transferring something more than just links isn't even realistic.) Reviewing top interesting links and acquiring the content from the network would be probably even encouraged by the content owners.

Now, if this would be built as an open extensible system, and somebody would built another extension that would start in certain cases to transmit media files directly to each other after passing the links (in cases where we can see that the two persons are remaining in the same room for a while), certainly you wouldn't expect any company to ship with something like that out of the box.

Then again. I see it like this: Means for copyright infringement are already enabled on all devices. I can do a lot of copyright infringement even on my N900, by downloading material, sending and sharing it. It isn't even very hard right now. I'm not convinced that whether something is easy or hard to do it more or less problematic. It's the users that choose to perform illegal actions with their devices, if they choose to do so.

Then again, an extensible plugin architecture might also spawn some completely new and wonderful use cases. For instance combining flavours of concept #4 here: I choose to share some high res pictures I have myself taken with the device to anyone interested. Them receiving these pictures would spawn a spark of creativity within themselves, and something new would be created as a result of combining media.