In the majority of cases involving drive failures, relying on a drive's S.M.A.R.T. status is merely a "feel good" measure which is unreliable at best.

Note, the freeware SMARTReporter is not to be confused with shareware like the $25 SMART Utility which claims to have an additional pre-fail algorithm built in to the app; however, I suspect that's tantamount to throwing good money down a rat hole since the Google analysis of over 100,000 drives reported "...models based on SMART parameters alone are unlikely to be useful for predicting individual drive failures" and "...it is unlikely that SMART data alone can be effectively used to build models that predict failures of individual drives."

If it were possible to effectively predict drive failures, the vast resources of the Google corporation R&D arm would have figured it out by now. Considering the thousands of drives used in their servers worldwide, it would certainly be in their best interests to do so.

http://labs.google.com/papers/disk_failures.pdf

Work at Google on over 100,000 drives has shown little overall predictive value of S.M.A.R.T. status as a whole, but suggests that certain sub-categories of information which some S.M.A.R.T. implementations track do correlate with actual failure rates – specifically, in the 60 days following the first scan error on a drive, the drive is, on average, 39 times more likely to fail than it would have been had no such error occurred. Also, first errors in reallocations, offline reallocations and probational counts are strongly correlated to higher probabilities of failure.