The 350ma I believe included the mouse and keyboard also. USB keyboards are like 25ma and USB mice are around 100ma for optical. I don't know what the power consumption of roller mice is, but lower than optical. This also was a development board that has extra stuff on the board that will not be on production boards. The board alone without the keyboard and mouse would be lower. if you set it to a task and then unplugged everything it would probably be 1watt. I think that 2.25watts that he tested it at with everything attached is phenomenal! I am figuring it at about 7.5watts with a USB HDD for continuous operation and adding in a surge due to the HDD up to 10 watts. It will probably be less! Never hurts to figure high and be wrong.
512MB version 2.0 as WordPress Server
Motorola Lapdock with Pi2B
Modded Rev 1.0 with pin headers at USB
(RS)Allied ships old stock to reward its Customers for long wait!