I can verify that class 10 does work in a DX, just not well. I didn't even think about it when I replaced my dead card (six months old and it died, WTF) with a 16 GB class 10 PNY. At random times apps will claim the card doesn't exist, even if I unmount then remount it; sometimes it takes a full reboot. Pretty annoyed at myself; I plan on picking up a class 4 or 6 SanDisk to replace it.