The servers will support up to 32 Xbox players at once, resulting in one of the larger Xbox 360 multiplayer shooters. Without a dedicated server, Section 8 only supports 16 players on the console. On the PC side, running the game on a dedicated server will allow for 40 players, with the max knocked down to 32 when moving to peer-to-peer.
Section 8's multiplayer component is an ambitious team-based game that's receiving comparisons to Tribes--which is quite a compliment. Might be worth checking out.