In my opinion, about the only way to get any data on lens reliability is find a source who has a lot of lenses, repairs them and keeps the statistics. Here's a link to a lens rental company and their repair statistics. By the way, if you were ever wondering how or where you could rent just about any lens, this is the place.

http://www.lensrentals.com/blo...ens-repair-data-2011

Additional information is here:

http://www.lensplay.com/lenses...s_defect_results.php