Justa Picker - I have a friend with the Merle Haggard model Martin - a 12 fret slothead with a cutaway - and he hasn't had any trouble keeping it in tune. Your milage may vary of course.

And Martin - You said
"I'm just curious about the volume thing. Seems to me bluegrass players are always looking for volume. Why does it seem you never see a bluegrass player playing a D28S?"

I suspect a lot of it is just tradition. Mandolin players play F-5's because Bill Monroe played one. I suspect bluegrass guitar players do the same thing. "If it was good enough for Lester Flatt it's good enough for me". I also suspect that many of them feel the need to have those extra two frets - even though they may never use them.