Never try ANTHING without a full backup.
I ran another Surface Test on a Toshiba (W7 Ultimate) laptop's 156GB HD [C: drive] which I already knew had "read errors" following several full backup attempts using Ocster Backup Pro.
Anyway, the Surface Test rattled along nicely for about an hour with the occasional error found - indicated by a red square, then the test slowed down considerably when it had to deal with a batch of about 15 errors, so that after 9 hours on-the-clock the program under test became unresponsive and the laptop went into hibernation mode. It would be nice if these errors could be fixed. Perhaps the paid for bootable disc version of Partition Wizard might be capable of this!