I have an Intel based iMac and a Macbook. The iMac is running 10.4.11 the Macbook is running 10.5.1. When plugging my new shuffle into the iMac, I have no problems. It more or less immediately recognizes the Shuffle and opens iTunes. Different story with the Macbook. It takes anywhere from 5-7 minutes to be acknowledged by the computer. Any attempts to move songs onto it are met with the beachball. When the song(s) are finally moved the Shuffle is ejected and the message in iTunes says there has been a problem synching and to disconnect it. It is up to date and I have restored it twice only to have the same problem.