Some.

Most people think that Ethernet controllers have a "burned in address" and that's that.

Not so. All Ethernet controllers can be instructed to use a different MAC address. This 'feature' of Ethernet was used by some networking protocol suites, DECnet and XNS in particular.

Linux and *BSD systems, which the majority of WiFi hackers will be running, make this very easy to do -- the ioctl() call is brought up to a shell-level command and you can just jam in the new MAC address from a command line:

http://en.wikipedia.org/wiki/MAC_address 

So someone who is willing to slug it out with one of your computers could hijack your MAC address by sniffing to discover your MAC address, then telling their WiFi card to use your MAC address, then they either slug it out with your WiFi node or wait for you to turn the node off and whaa-la, they're in like Flynn.