I found a nice little article on MAC address filtering for WAPs on Techrepublic . You have to register to see the full article, but it's free and well worth it! Tech Republic is a great community to belong to. The link is here to get to the site, and I have posted a good portion of the article below:

An open door to intruders
The problem comes when an intruder wants to gain access to your network and has decided to sniff your wireless network traffic. Sitting in your parking lot or some other easily accessible location, an intruder armed with the right hardware and software can easily sniff your wireless network and capture all packets sent to and from your access points. The captured data packets contain all the information the intruder needs to make a connection to your wireless LAN. This information includes the following:

Authorized MAC addresses
IP addresses
IP subnets
Wireless LAN SSIDs

The intruder can easily configure a wireless device with a captured IP address and subnet in the device’s TCP/IP Properties window. Configuring captured SSIDs varies from one type of NIC to another, but it’s done from within the configuration software provided with the NIC—again, a very easy configuration to make.