"Something you might find interesting: security based on the MAC address of a PCMCIA card is not secure."

The response I sent on to them, and which I wanted to share here, is:

Yep. I was aware that it's not a bulletproof answer. Even on my Macintosh, I can set the MAC addr that my aiport card should use. However, in order to exploit this, you have to have the software to snoop the network without having joined it, determine a MAC addr in use, spoof it. The hard part is finding out the MAC addr to use. In order to do this, you aren't just trying to join the network in a normal fashion. And then as soon as you do, one of the machines with a MAC addr in use gets knocked off -- and its pretty clear to the user on the network what is happening.

The only way this is really useful is if you determine the MAC addr to use and then only use it when I'm not home. If you are doing that, then I've got much more to fear from you then you getting on my network. Stalker Alert! :)

All I'm after with using this scheme is really a way to keep my neighbors from jumping on my network segment and using my bandwidth. My neighbors aren't anywhere close to this good. :) However in case they are, even behind my NAT, I don't run anything in the clear that I care about (heavy use of SSH).

After all, this really isn't about security, but access control -- at least a decent attempt of it.
I submit that if you want real security, don't use wireless. If they are good (or evil depending on your view) enough to work around your MAC addr control and wait till you aren't home, then they probably have already found a way to break into your house (remember the range of wireless devices isn't high) and could snoop your ethernet cables as well. Or just take off with your computers and peruse you hard drive at their leisure.