I forgot to mention though that there are very advanced attacks that can fingerprint wireless cards regardless of their MAC address. It is totally possible to uniquely identify WiFi cards if you can get a live sample from them, in some cases maybe even router logs are enough I dunno. Anyway, it is in the realm of possibility for the NSA to have much of the USA covered in spectrum analyzers that could perhaps even fingerprint your wireless card regardless of its MAC address. This is definitely in the realm of possibility, but it is also definitely in the realm of the NSA (ie: not the FBI).