I did a big "seat of the pants" analysis on network bandwidth with 100ish players a month or so ago in one of these forums, once you start pushing 100 player pawns, the network data (using the default configurations) would make a game pretty much unplayable unless everyone's on Gigabit ethernet. Of course, if you're not doing an Unreal style game that requires extremely fast network updating, you can adjust lots of settings downward to decrease the amount of bandwidth.
Some guys tried to do some ArmA 128 player servers, it was blowing up their server link completely.
Of course, you can spawn as many bots as you want into a game, as many AI controlled pawns, whatever, but the networking updates will kill you after a while.
You can also cut down on latency by not using pawns where you don't need to (but in doing so you'll also lose the benefit of prediction, but this is generally not as necessary with AI, since they are not strictly unpredictable like players).