I'm working on something similar, or have been rather on and off. Instead of MSSQL, I use MySQL. It works flawlessly except for the fact that the .dll can be read if the client gets hold of the jampgame file. So distribution would not go well, lol. I need a way of encrypting it somehow so that no one can read the username and password of the server. Otherwhise I already have a working mod.
It reads and writes certain things to the database. It writes flag captures, flag returns, assists, deaths, kills, duel wins, duel losses, siege objectives completed, etc. Each client makes their own account which is linked to a phpBB2 forum so that once you register in-game you can use that account on the forums, and if you register on the forums, you can use that account in-game. It works both ways since the same database is attached.
The game server can be completely seperate from the MySQL server, and the MySQL server can be completely seperate from the phpBB2 server. So the ease on the bandwidth is easy to maintain. The clients and the server CAN feel lag spikes however since the server needs to communicate with the MySQL server, however, if you want you can put the MySQL and game server on the same box and you wont feel any lag. The lag spikes only happen when a client logs into their account since thats almost the only time it needs to update or insert information. Also the information is logged when they disconnect so you could feel it then as well.
If you're interested in helping me with this project, we could eventually finish it.
BTW - I talked to the author of BWN, he uses a seperate application to insert the information, and its not to a database, its only to some files which the server reads and writes. It's rather small.