Back for Quake III, they said 30K tris for singleplayer, and 15K tris for multiplayer.
However, systems running JO and soon JA can handle much more. Around 40K or more tris is acceptable, and mutliplayer could hover around 20K to 30K.
Clarionet, n. An instrument of torture operated by a person with cotton in his ears. There are two instruments that are worse than a clarionet -- two clarionets.