This probably isn't the most fitting topic for this, but I imagine it will be the most effective:
I did some house cleaning of my XBL Friends List, and of 86 people, 14 being online, only 1 is playing Halo 3. Personally, I'm not done playing this game yet, but I like to party up. So if anyone is playing this game in multi a lot, add me as a friend. I always like to party up, and I'll play anything (preferably matchmaking or custom games, but I'll play the campaign too). For now I play pretty much every night. I'm east cost.
On kind of that note, I really love matchmaking, but I'm going to agree with those that say the game needs a server browser. If it had one, I'd use it to find custom games, but I'd still go into matchmaking for everything else. Say I've got a full friend's list, and 20% of them are online, and half of them are playing Halo 3... even with 10 people (which I had daily back at launch), custom games are difficult because only 1 or 2 of those are going to be in a position to join. I just don't see how it's supposed to work without scheduling a game time, which really seems counter to the rest of the Halo 3 philosophy. At the very least, the game desperately needs clan support, to at least get over the friends list limitations.