mac spoof hack arp broadcast

I have long taken the time to set a mac address filter in my wireless lan just to make it next to impossible for someone to gain access to my wireless lan since I only put mac addresses of trusted computers in the list. Recently, I told someone what I did and he said - Well, what is to prevent a device from listening to arp broadcasts and then spoofing one of those. That would defeat your mac filter, wouldn't it?

I thought it was a good question so I pose it here to those that know more about how wireless works to "discover" devices on the network. Could this be done? Have there been reports of anyone doing this?

thanks,

Vern