I've used MAC address control limiting ever since I've had Broadband and haven't had any problems. But I tried to set up WEP and had no end of difficulty. Once I'd got the wireless router into a WEP-enabled state, even though I put the correct key into the laptop I couldn't get the thing to reconnect. As the control software for the router is in the laptop, eventually I had to system restore in order to get back to a non-WEP state.
How (and why) would anyone discover the MAC address of an in-use laptop without having access to that laptop? Presumably anyone doing so in order to access a private wireless router without permission would be acting unlawfully?