My WD Scorpio Black 750GB had a 1 or 2 pending sector count, and then HDD regenerator made it magically go away. The pending sector count rose to '1' every few months and I used HDD regenerator again each time and it went away. It didn't always turn into a reallocated sector but a few did.
Anyway, one night overnight, the drive took a dump. Bad sectors everywhere!
So, keep an eye on it, perform a write based surface test such as spinrite or a disk wiping program (I'd suggest hdd regenerator as a last resort), Microsoft's chkdsk is only a read surface test. Also, of course have a backup as you always should with any drive.