This subject was talked about in tonight's Ubuntu hour.. I found this article on how to do it.

Today, users run their notebooks everywhere. To stay connected you use the local wifi to access the internet, on the couch at home or in a little cafe with your favorite coffee. But modern hotspots track you based on your MAC address, an address that is unique per network card, and in this way identifies your device. Read more below about how to avoid this kind of tracking.

Why is this a problem? Many people use the word “privacy” to talk about this issue. But the concern is not about someone accessing the private contents of your laptop (that’s a separate issue). Instead, it’s about legibility — in simple terms, the ability to be easily counted and tracked. You can and should read more  about legibility. But the bottom line is legibility gives the tracker power over the tracked. For instance, timed WiFi leases at the airport can only be enforced when you’re legible.

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