i have SanDisk 6GB microsdhc card. Had same issues listed above, but successfully formatted it (as FAT32) using SDFormatter and loaded music while attached to computer using SanDisk's USB adapter and Windows Explorer to copy over files (blackberry's Media Manager tool didn't work for me). Put the sd back in the blackberry and it worked!!!

(I listened to music files for a few hours - like an iPod!)....THEN after a reboot of my blackberry i get an error
"A Media Card has been inserted that contains errors. To correct errors please use a disk error-checking utility on a computer.".

Anyone have a workaround for this? I'm on OS v 4.2.2.89 (platform 2.4.0.39) if it is relevant. I could reformat repeatedly (did twice already), but it's not worth it, need a solution that sticks...