OK my new mouse that came with my new 27" iMac needed charging. Big FAIL on Apple's design, the port is on the underside of the mouse and you CANNOT use it whilst it is charging! Come on Apple, old style USB mouses had the cable at the back, why on earth put the charging port underneath and then disable the mouse? Fortunately I did have an "old fashioned" mouse I could use whilst the new one was charging, but I feel sorry for anyone who does not have a 'spare' mouse to use, as this effective means you cannot use your iMac either!!!