A while ago we were shooting at a pumpking patch and got about 180+ shots on a cloudy Saturday. Everything went great until I got home and downloaded the pictures.
To my surprise most of the pictures had a 'soft' look and I spent most of the afternoon shooting in a controlled environment to make sure there was no camera shake to blame and then most of the night doing a lens calibration or microadjustment for each one of my lenses... needless to say, frustraded and sleep deprived I called Canon Customer service and I was told to reset my camera to factory defaults and test using one of my 'sharpest' prime lenses if possible. I did and hours later I was shipping my camera for repairs.
At least I was shooting my kids and not a paying client, should that have been the case the liability would increase exponentially

Now the real question is... Why didn't I notice the 'softness' before? Well, I shot a series of family shots and because I was shooting in my home studio I was using strobes and my apertures were about F11 or smaller and of course everything was in focus. At the Pumkin Patch I was shooting with my lens wide open at F2.8 for the most bokeh and to separate the kids from the people around. I know, I know... I got fooled by the LCD and what I thought were 'in focus' shots were...'soft'

Lessons learned? I was glad I had registered my camera and my lenses at the Canon Web site and I had scanned the receipts/invoices for warranty repair. Next time I will make sure I spend the whole morning/afternoon testing new equipment and do exactly as I preach :)

However, the best advice I can share is to always have backups and redundant equipment for times like this. I had a couple of shootings that would not be possible if I had no backup camera while my 'main' camera is in the hospital for open surgery