Bl4ckSh33p
Part of larger more robust systems say guild wars/ WoW will also use partition trees such as quad trees. These can also be used in the network to determine who get's messages and who needs to recieve messages. C2 super duper easy to use system however sacrifises flexibity for ease of use. However you can still use C2 MP core functionality to continue to do so.
For me the MP did not do the required job. So I work around it. I also structured my game to work more like a PSO rather than WoW. Where there is a shared lobby, but when the players advenure together then it's changed. This is pretty easy stuff. Players leave Room and join Team Leader Hosted room when they enter the dungeon.
I found a lot of work arounds that I'm happy with. So I have no blockers to create MMO's, however this does require more work than just simple click and drag.
My Derelict Project(sig) goes into this. When I have the time to work on it. It's been a couple of months. but I will be back. The server system is down so you can't click and try. plus people need to actually be playing to really see MP work maybe someday.