Keep in mind that TCP/IP games are horribly slow in distributing and collecting turns once you get past 2 or 3 players. With 2, it goes as fast as or faster than PBW. But with 3 or more, it gets slower and slower. This is because the game will only send out turn files to one player at a time. With PBW/PBEM (or even manual file transfers over AIM or something), you can send the turn files out to all players at once. The games get really slow on TCP/IP when you hvae 8+ players.
Now, organized game sessions are still a great idea, I am just not sure that using the TCP/IP mode is the best way to go.