Thanks for that explanation as well, it is much appreciated. Thanks to both of you gentlemen I now know a bit more about FETs and am very thankful for it.
Most of the really usefull applicaitions for fets (or IGBTs for that matter) is not in knowing how to use ONE but knowing how to use MANY. An RC ESC (Electronic Speed Control) that can deliver more than 100A @34V, is a stack of pcbs with dozens of little tiny fets on it each with a very low internal resistance. Larger parallel fet (or IGBT) circuits can deliver hundreds of kw of power.
It's probably worth your while to get a handful of fets of different sizes off ebay and just play around with them, switching lights, relays, motors, piezo alarms, laser diodes, or anything you can think of. Remember to do the math first XD.