So Jesse (one of the founders of opscode (makers of chef)) used to work at amazon before he founded chef along with Adam. Adam had been working almost 2 years using puppet at other companies and it was pretty obvious he wasn't happy with the way puppet did things. I've heard that chef was closer to the method of thinking that amazon employed in their automated operations (which wasn't really exposed to the public). That being said, they're both fine solutions and are in use in a number of large enterprises (goog, etc.)...the key is to be automating your operations in some manner. Hell...use both and see which aspects are / are not important to you / your people.

here is my view on the topic http://devopsanywhere.blogspot.it/2011/10/puppet-vs-chef-fig...