One of the risks that affects all wireless deployments, large or small, is the fact that wireless signals don't stop at your walls. Setting up an AP is kind of like putting an RJ45 Ethernet jack in your parking lot. Attackers can just walk up, “plug in” (associate), and connect to your network. In fact, you don't even need to be in the parking lot. With the right gear and line-of-sight, you can pick up Wi-Fi signals 20-25 miles away. It's not a trivial task, but with amplifiers and high-gain antennas, it's possible to eavesdrop on wireless networks from very far away.
Peter Shipley in San Francisco performed some of the earliest wireless security experiments (http://www.dis.org/filez/openlans.pdf ...