Apple has announced a replacement program for 1TB Seagate hard drives on some iMac systems sold between October 2009 and July of 2011. The drives in question apparently have a higher chance of failure than they should, and Apple's replacement program will allow affected customers to get the drive replaced for free at Apple or an Authorized Service Provider (AASP).
Apple said it is contacting customers it believes bought affected iMacs, but that contact is limited to those who provided a legitimate (and still-working) email address when they registered their iMac. The company also has a serial number checker that allows you to check even if you haven't heard from the company.
the company is warning users that, "You will need to have the original OS installation discs that were shipped with your product in order to re-install your operating system, other applications and any backed up data after your hard drive is replaced."
The company also has a process in place for refunds for customers who have already paid to have these drives replaced, saying, "If you believe you have paid for a repair or replacement due to this issue, contact Apple regarding a refund."
The program is limited to 1TB Seagate drives in iMacs sold during the specified time period above.