Here is some good starting points for reading on WLAN and security that I and my colleague found on the net.
http://www.cs.umd.edu/~waa/wireless.pdf
http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html
In our opinion, we think its scary that we already have seen "proof of concept" of several WLANs that have been insecure, especially those default installations, that we have seen a lot of in real life.
