Is there a way to keep a USB port powered while the machine is off? I have a wireless mouse that I would like to charge while not using without keeping the PC on. I know a powered USB hub will do the trick, but would like to not go that route if possible with the DX58SO2 motherboard.
Probably not, unless there is a BIOS setting that controls power to the USB ports. It will depend on your board. Some boards provide power to the USB ports with the system off. Also, check the Intel product guide, for your board, +5 V Standby Power Indicator. There may be a description of where 5 V standby power is availble on the board with the system off. For the DX58SO, standby power is available at the memory slots and the PCI bus connectors.
Check the product technical manual for the DX58SO2.