My Dad has an issue with his 21.5 imac bought in october of '11 with usb thumb drives. I tried logging into the diag partition and no response, just like with disk utility and sys profiler. Tier 2 phone support stated to bring it in to the store. after showing the genius the issue, i brought the thumb drive to other 21.5 and 27 inch imacs..... guess what same issue. drive does not show up. pop it into a mini next to it and bang, its found.. i have a support case open with apple and its supposed to have gone to a engineer in Cali. fyi, tried pny, sandisk, and lexmark all the same... but external hard drive, printer, and UPS all work fine on USB, and the drives work fine in my MBP. has anyone else experienced this????