Basssed GBATemp, I don't know if you've remember, but I was talking about another fourm site that was very similar to this one that had different moderation rules, and just learned today that they're limiting their Group DMs to 5 users, and the messages contained in a PM to 15,000 messages (including you and the other person)
GBAtemp.net - The Independent Video Game Community
DragonMals
Their reason for making their limits is because they're making the foums more about the public discussion about their games rather than a whole chatting place and such. Meanwhile we have our own IRC chat and lenient PMs.
- max limit is 50 users
- kicking/leaving users doesn't free up a slot, apparently
- it works