pwillard:
I think what you fail to realise is that the sparkfun board will create SIGNALS that can used with higher voltage logic. This is NOT a driver board and it will fail to provide much of anything in the way of high side "current". You CAN use this board to drive higher voltage rated MOSFETS. You should consider that.So... the board outputs SIGNALS of GND and HV Voltage to be further used as needed to "drive" your loads with "something" suited to "driving loads".
Think of it more like an optically isolated level converter.
Oh 
thank you. I think then I completely misunderstood their description. I thought when they wrote
"We often use this board to allow a microcontroller control servos or other motors that use a higher voltage than the TTL logic on the (3.3V or 5V) micro, and may cause electromagnetic interferance with our system as the motors turn on and off. "
they meant I can use it for switching my 12V power circuit.
Then I will need to look for another component which can switch the 12V+ line with my 5V from the Arduino. Do you maybe have any suggestions?