Apple hasn't confirmed this but it appears as though there's a widespread problem with the 24" iMac shipped with the optional 500 GB HD's. I've had a huge problem with my 24" iMac and it turns out that its 500 GB is corrupt, and the incident is far from isolated. The technician told me that it could take weeks before they could retrieve a "healthy" model. He furthermore told me that he's contacted Apple several times but they have failed to send a replacement unit because there's such high demand for it. The French site hardmac.com also reports that Apple has a problem with shipping "healthy" 500 GB HD replacements. If you're planning on purchasing a 24" iMac with a 500 GB HD, consider the other HD options because you'll most likely encounter HD problems.