Checking the S.M.A.R.T status alone in disk utility is not always best to determine if the HDD is failing. I had a Seagate 7200.4 RPM that was failing, disk utility said that the S.M.A.R.T status was verified. I found it that it was failing because the laptop would freeze randomly when doing simple tasks, such as opening safari, mail, etc. I would hear the HDD click randomly when the laptop is left idling, I could hear it speed up and speed down. Also, when you try to repair the HDD using disk utility and it fails to do so and says something like "invalid node structure," it could also mean that there is something wrong with your HDD. Starting up the laptop can also take as long as 10min or it can not start up at all unless you go through safe mode. If you haven't had any of these symptoms, you should be fine.