<i>Almost no committed code that is commented out</i><p>I don't 100% agree with this one, at a company I worked at they had a policy of commenting out code, adding a date it was commented out and a reason why. After 90 days aging it would be removed by a script, which would delete the commented out code, grab the description of why it was removed and then do a commit to source control with the description. This actually worked great for documentation of changes that occurred. Now granted you can do the same thing by requiring comments on commits in source control and then researching the version history. But having it right there in the code made the process of investigating code very fluid.