The Washington Post Blog, has published an article about two hackers who have reportedly demonstrated a flaw in the MacBook's device driver for the Airport card which would allow complete control of the system.
...this attack can be carried out whether or not a vulnerable targeted laptop connects with a local wireless network. It is, they said, enough for a vulnerable machine to have its wireless card active for such an attack to be successful.
The vulnerability appears to be an issue with Atheros, the makers of the Airport card rather than Apple directly.
[Update] It seems after further investigation that the hack was performed on an external USB connected wireless card which means that almost anyone using a MacBook is not a risk from this exploit.