This is is relatively old news now, but
this white paper from Google labs is still the most extensive and comprehensive study of disk drive failure available. Among other things, it analyzes the value of S.M.A.R.T. as a predictor of impending drive failure and concludes that S.M.A.R.T. is much better at telling you when a drive has failed than predicting when it will fail. They fault the drive manufacturers choice of tolerance settings for S.M.A.R.T.'s poor predictive results.
Their conclusion is the best predictor of impending drive failure is a surface scan such as TTP or Drive Genius can perform. Unfortunately a full surface scan takes a
long time to perform.
FWIW, one feature of TTP's S.M.A.R.T. report I like is its reporting of the individual parameters and not just the summary verified/failed of Disk Utility and most other utilities that rely on the same results as DU does.
