I've read through the various posts here and the common wisdom is that off flavors are because of poor sanitizing or using scratched plastic carboys/buckets. I'd like to read from some of the "master brewers" here and get their take on this commonly held notion.

Here is the basis for my question:

1. Palmer's reference has very few off flavors that he mentions as a function of cleaning and none from using scratched fermenters. So, if you know that you are using proper sanitizing technique, have you still produced off flavors? If so, were you able to track down the source as something different than Palmer's observations?
2. Another commonly held notion is that glass is better than plastic because plastic scratches and these become sources of infection and off flavors. Have you ever had this happen with scratched plastic carboys when you knew that you sanitized properly at the beginning?