This can be a dilemma for people designing and building commerical shields for the standard arduino pin layout. If a shield is designed and built to require more then 50ma on the 3.3v pin and is plugged into any arduino board that uses a FTDI chip rather then the newer Uno or mega2560, then there is real possibility of damage to the FTDI chip on the board. So vendors will have to be awful careful how they document their shields requirements or there may be a lot of not happy users.
The new extra 3.3v current capacity for the uno is nice, but there must be cautions understood and obeyed.
Lefty