I have a drive in that system I got last Tuesday where it's fitness is apparently null. However, the machine seems to run like a charm.
SMART is a nice feature to have. Yes, it can misdiagnose, but I'd listen to it... If it's bugging you, run some tests. Whatever brand drive you have should have some diagnostic software available. Run the extended tests and see what pops up. And be sure they are NON-destructive If you have a problem, maybe you can RMA the drive. Maxtor had something where they'd send you the new drive then you return the old in the same box... If that's an option, you could copy your data then have a fresh new drive.
Double check the results with Hutil, it's samsungs drive testing utility. It wont tell you the individual attributes but it will tell you if it passes SMART and other tests.
It is strongly recommended to back up the user's significant data in advance because Hutil has a Write operation that can erase it. Samsung has no responsibility of lost data.
Don't run the write commands then, the self diagnostic shouldn't be data destructive. The 'ERASE HD' and 'SET MAX ADDRESS' commands destroy the data, don't run them. If you are still worried about it this tool doesn't have any destructive options.