Got 12 here at work for various purposes. Two on one SSID on the corporate network for roaming, and a bunch of others for different departments to run their own isolated test environments.
It gets a bit hairy at times when you want to do testing that requires a noise-free spectrum.
It's normally only 11, but we've got an extra one set up at the moment. Our "show guy" is setting up the environment he's taking to Bingoworld in May.
We also have a number of 900MHz transmitters, but those don't broadcast in a way that can be seen by anything but one of our own handsets.