If you somehow happened to miss the new stories about failing Seagate drivers on various tech sites recently.. basically an unusually large number of Seagate 500gb, 1TB and 1.5TB drives have been failing within 3-6 months.
Seagate has finally identified a firmware problem with serveral models of their .11 range.
See this Seagate KB for details:
http://seagate.custkb.com/seagate/crm/selfservice/search.jsp?DocId=207931
I'd recommended if you have drives of the models noted in the KB you update your firmware before they randomly decided to freeze up one day when you boot.

