Our board is very active, so having an IM system would help cut down on some of the useless posts and PM's that fill up the db.
It would have to be understood that if someone were to purchase the IM/Chat plugin, that it would be resource intensive. We would still be willing to purchase it, and even get a faster dedicated server. Our community is quite intense, as people use it to meet other members in their local areas. For us, it would make sense to buy it, and upgrade the server if necessary.
Thanks for your consideration...