QUOTE(SueHM @ Sep 26 2009, 10:56 PM)

I think a natural followed by a sharp is a somewhat old fashioned way (although to my mind clearer) of saying that you want the note to be a sharp, rather than a double sharp. However the more modern way of doing it is simply to put a sharp in front of the note in question.
I agree with this. Natural followed by sharp is the older way to do it, just a sharp on its own is more modern (although some may still use the first method). Both are pretty unambiguous, I think, so it doesn't matter that much which you use, I'd go for the modern method - less cluttered.
QUOTE(river @ Sep 27 2009, 12:49 PM)

F

and G are not the same note, except on a tempered instrument like a piano or guitar.
Right, but even on piano and guitar, there is still a theoretical difference. In piano music it does usually matter whether something is written as F# or Gb.