Chris Butcher from Bungie gave this presentation. This was talking about how matchmaking works in H2/H3 and differences (goods and bads) of both.
This was a pretty technical talk about the internals of the matchmaking process. Chris started by talking about why this is needed. The idea of user being matched in games that will be fun (not too easy or hard) with some way to hold the user and keep them playing.
The problem with H2 matchmaking was that is was based heavily on skill. The cheaters who had figured out ways to break the system created bad experiences for typical users.
With H3, the team worked with Microsoft (Research) to use the TrueSkill and integrate this into their matchmaking to make this process seamless and transparent to users. This is a pretty complex system based on a bayasien algorithm to compute the players real skill. This combined with some somewhat complex networking code pulls off the matchmaking we are now using with H3. Chris presented results with > 80% of all Halo users playing over 100 multiplayer games. This is a pretty substantial improvement over H2.
Problems with the new system are the complexity can confuse users (as they don't get to see the under the cover working going on, nor would most understand it).
I will post the slides when available (Feb 25th).