Spoofing mac addresses is easy, on a scale of 1 to 5 with 5 being the most amount of knowledge needed to complete an intrusion attempt activity; I would rate it at 2. The factor in your favor is, the person has to be within range of the antenna to do anything. If you’re a high value target, I would think twice. I have a couple of decent papers I can did up, but just type "spoofing mac address" in google. Securing wireless connection by mac lockout is over rated. WEP has been all but made obsolete by cracker software and the method of authentication/communication is well documented. The real danger in wep is (my opinion) sniffing. An open wireless router easily becomes a funnel for sensitive information and depending on the motive of those listening, they may never make a move to give away their intention and set on it listening to email, authentication etc. I am discussing this from a point of view that sensitive information is not worth the risk of convenience. Wireless access should be segmented, like already pointed out. If it's your house, no big woop you can watch the connections but in a large environment that becomes difficult when compared with the benefit.