Hi, i've been playing a bit with the MiniUSB and reading the page (menu Hardware -> MiniUSB) i wasn't able to easily figure out what the jumper was for.
I downloaded the schematic and found it is for enabling/disabling the 5V output of the card.
I also downloaded the FT232R datasheet to figure out that the 3.3V output supports up to 50mA.
I think it will be good if this info is rigth there on the page.
Regards!