In my early climbing days I was taught that dropped carabiners could develop microscopic cracks making them (at least potentially) unsafe. My reasoning since then has always been "potentially unsafe = unsafe"

This article questions that conventional wisdom, although I note the small sample size. Just wondering what others think and what other testing information you may have come across.

http://fatcanyoners.org/bush-guide/dropped-carabiners/

Through ingrained habit and cowardice, I think I'll continue to err on the side of caution, not that I do much rockclimbing anymore.

edit: Some more mythbusting that I hadn't seen:
http://www.geir.com/mythbuster.html