Always... ALWAYS at the very least duplicate your most important data that cannot be recovered from elsewhere. Every computer should have a warning sticker on it.
Last weekend I returned a 500 Gb Samsung drive since it's SMART was reporting pre-failure at B8 'vendor specific'. It used to be at a normal value, but then began to degrade. I didn't notice anything in use, but returned it since I can't be confident of such drive keeping my data "safe" for any lenght of time.
Now I hope it wouldn't bounce back from the store due to the undefined SMART parameter and there being no apparent failures, because then I would have to cover the inspection costs, but I still wouldn't have any use for a drive that I cannot trust any longer.
I was actually refunded for it's full retail value from nearly 2 years back, when such a drive's cost was twice more than today. I was expecting to receive a new comparable HDD model, most likely a slightly upgraded version of the same series. Profit of 70 bucks, but that's not enough to cover the time and trouble I spent to mirror the hard drive on a new drive. Doing a job for the same time would been more profitable and most likely less stressful. I did also overwrite the hard drive to erase all the data in it.
Before this I've had one HDD failure, that was not just a pre-failure. 15 Gb Maxtor drive experienced a bearing failure, at least that's how it sounded like, a very loud constant noise coming from the hard drive. Regardless, it was still functioning and I was able to copy everything from it. It happened a few days prior to the expiration of warranty. Got back a 30 Gb drive.
This Samsung drive actually was my first other than Maxtor hard drive in 16 years. Last year I bought another Samsung drive, the slightly upgraded model of the series. Last week I bought the first WD, to replace the returned drive. Originally I considered buying a new Samsung drive, but decided to give a try for WD. The samsung drives are less noisy, although this WD isn't really bugging me either. They don't kid you when they claim that the Samsung drives are quiet.