1).  Proxies which use multi-layered encryption so that only the source and destination nodes what is being sent (the middle proxy nodes only know who they are receiving from and sending to, not the content). This they got from Tor.

2).  Encrypted data caching so that the number of anonymizing nodes between you and the content you want doesn’t unneccesarily slow down transfer speeds.  This they got from freenet.

3).  Some fancy algorithm in the client that looks at the hashes in your library and can then determine your tastes.  The algorithm then will group you with other nodes with similar tastes.  This is important for maintaining fast data speeds while maintaining downloading.

4).  The ability to communicate with other nodes about the quality of material on the network.  This is important to block spam

5).  A karma system that makes your downloads and uploads faster if you donate more hard drive space for caching anonymous data and for providing bandwidth for proxying other peoples data anonymously.  With out this karma system the fear is that leechers will swamp the system.

There is still the problem of making the tribler network backwards compatible with normal bitorrent network.  To do this safely nodes that interface between the bitorrent and tribler networks will either have to be using a vpn or be located in a bitorrent friendly country (Denmark, Sweden, Switzerland).  You could imagine the providing this more dangerous and specialized service for the tribler network will yield you more karma. 

Ultimately if tribler is as kick ass as the test network indicates it is the new standard being developed will yield a network that will slowly dominate the sharing space :)  At that point less interfacing nodes (nodes that send and recieve data from outside the tribler network). 

The real genius of tribler is that they found a way to create the karma system which makes the whole system convenient enough for people use to fast downloads.  That and the social comment/annotation system which prevents spam.  Rather than being a shitty mashup between bitorrent and facebook, the social element is central to the succesful functioning a a decentralized filesharing system.

i would say the cache has to be encrypted not the stream…