I have to agree with some of the others. As soon as a drive starts doing "iffy" stuff such as screwing either with smart status, or showing "Failed" then going back to "Verified" I would chuck that drive. It may be a fluke, but do you really want to trust your data or a running config on a drive that can possibly crash, or worse, fry the controller chipset on the Mac/PC that you are using?

Anytime a drive exhibits symptoms that makes me second guess as to whether I should chuck it or keep it, it automatically gets chucked because I don't want to be wrong and it goes bad.

I just chucked 2 HDDs today because one of them was a bit iffy (sometimes windows wouldn't start up, sometimes it would, but the system info logger was recording "Could not read. Bad Blocks") and the other I wasn't sure about, but I had issues with getting windows to stay loaded on the drive upon actually getting it up. Windows error's reported issue reading from the kernel. So both got wiped over 7x and recycled (I don't believe in just throwing them out. The metal and components can be recycled)

So when it doubt, always chuck the drive. Better to be safe than sorry.