function keys- few programs use them but they serve on my netbook for things like brightening and dimming the screen, locking the screen, ajusting sound levels, etc
caps lock- a few games use it and there are situations were it is legitimatly used (some have pointed out database programming)
windows key- i use that one because of its lack of use, its my push to talk button in teamspeak since it seams to have no other use
menu key- it can die