Strumelia:
Yes...high D. I played a low D that Guy had and loved it, but we went with getting two high D's for what one of the low D's would have cost. They are great whistles. The major scale vs pentatonic minor scale is definitely a big difference between whistle and NAF. Another difference is tone. The Native flute tends to be a much warmer/darker sound and less shrill. Both tones have a place in folk music, but either can be better suited for specific settings. There is also a notion out there that Native flutes cannot play a major scale, but they can if you learn a few fingerings above the standard/basic fingering charts. Hammered dulcimer player supreme Ilace Mears asked me to play a bass NAF on a Celtic tune she was performing at Evart a few weeks ago because she really wanted that dark sound. No one protested so I guess that it went over okay lol. Like so many parts of folk music, there is a place for just about anything. The key (to me) is just to pursue the sound that is rolling around in your head. Karen and I have even used tuba and didgeridoo with mountain dulcimer in the past, so we're pretty open to trying stuff lol.
John, do you mean in high D? (not low D)
John, can you outline the differences between Native American flutes and pennywhistles, assuming two that are in the same or similar key/size ?
Anybody here still active and playing their pennywhistles? 
Speaking of which, did you hear about the dyslexic who walked into a bra? 
