There was a problem with the Seagate 7200.11 series a couple years ago. The problem was fixed with a firmware upgrade. This is still ingrained in lot of peoples memories. A lot of these drives are still running and failing as we speak. You can include these in your sample data or you can ignore them, depending on your viewpoint.
http://www.theinquirer.net/inquirer/...200-11-failing
The 7200.11s being sold now should all be OK.