not crazy necro, but still.
I just got a Patriot LX Series Class 10 8gb card
It tested 9.9MB/sec write, 25.6MB/sec reading with the free "SD Tools" benchmark tool from android market (on my Nook Color running Gingerbread)
Good times! :)
I get to:
"adb shell mount -o remount,rw /dev/block/mmcblk0p5 /system"
and I get device not found. system already had nook color drivers installed and it worked for USB/etc.
I have rooted and flashed froyo onto the eMMC already.
Do I need to have an CD card in the thing? Too tired... ZZZZ