Macbooks can be grounded, too. The round metal thing that's holding the plug in place also serves as a connection for ground. It is moot if you're using the sma

Macbooks can be grounded, too. The round metal thing that's holding the plug in place also serves as a connection for ground. It is moot if you're using the small plug which doesn't have ground but if you connect the cable instead of the plug, or use a UK plug, the computer is properly grounded.