Hate to say it but I have no "real" problems with it. I can transfer folders with no issue to the player from my iMac. Are you folks trying to move many many folders at one time? Don't. Just pull over one or a few at a time. I've got maybe 125gb on my internal and 120gb on my 200gb card. I pulled about six-eight folders at a time over when I bought my 240SS with no issues. It barfed when I tried to move the entire Music folder, so I just worked my way through all of them. Took about 3-4 hours for 125gb. I have no issues with my card plugged into the device for normal transfers. I did use a card reader when I migrated over to the 240SS from my 120ll.
If you have issues try a couple of things. Restart the Mac. Make sure you are using the supplied AK USB cord. Organize your stuff so it goes in smoothly. Mine is in folders by Artist with individual albums nested inside them.
I do get the occasional barf, but unplugging and replugging the AK is all I have to do. I can transfer an album of FLAC (700mb) in a couple of minutes. A two gb hi-res folder might take a bit more than four minutes.
Im trying to load 6000 songs... which is beyond tedious. Try the newer version of AFT and see if its better for you next time.