Obsolete; only uses old US measurement units and cannot be used in the rest of the world with standard international metric measurements! Will check again in a few years to see if it is catching up.

After weeks of increasing crashes, spinning beachball, lost or changed preferences etc, and having tried all the recomended tricks of the trade, I was about to murder my Intel iMac when Apple HardWare Test (run all night in extended and looping mode), TechTool Pro Deluxe, Disk Utility (for Verification as well as Permission Repair), Disk Warrior (for Directory), S.M.A.R.T. status tests and the other maintenance standbys like Onyx,Cocktail, Macaroni, Yasu, etc, EVERY ONE assured me that the drive was, or appeared to be, OK. I had just grudgingly updated to Drive Genius 3 and let it run automatically on DrivePulse; it told me the drive had two bad blocks. A second run confirmed this and I zeroed the drive and reinstalled from Time Machine. Drive Genius said no bad blocks; better performance for a couple of days then deterioration. Tested again with DG ; 9 bad blocks. Discussed with very helpful support at Prosoft, and the resulting accumulation of tests and reports convinced AppleCare to replace the drive under warranty. By this time the TimeMachine backups were becoming corrupted which took a few extra hours after re-installation, but after which a smart, fast, perfect iMac is still showing no bad blocks.
I wouldn't be without Drive Genius now.