As part of their month-long Halo 3 marathon, 1UP sat down with a few Bungie developers to talk up the upgrades being made to the upcoming shooter's online matchmaking system. The central focus of their system will be parties and how to get your friends to play with you in both ranked and unranked matches. This method differs from the current XBL king Gears of War, which does not (officially) allow friends to play ranked matches together.
Gears developer Epic has stated that the reason its title lacks a clan-friendly matchmaking system for ranked play is Microsoft's certification process. Bungie producer Allen Murray counters that notion in the interview, however, by explaining that Microsoft does allow parties of friends in ranked matches but does "not provide that feature as part of the core set of matchmaking services." In other words, it's up to the developer to program the system, and Bungie feels it has learned enough from its Halo 2 experience to optimize the system they already have in place.
The interview talks a lot about custom rules matches and their efforts to promote the play. There aren't a lot of specifics, and much of what is said is subject to change between now and then. If you want to get a feel for the general design philosophy Bungie has, this should satiate you.