If programmers wanted to be technical writers, they probably would be technical writers and not programmers. You can see that tautology played out in many a Drupal module where the documentation (most likely a README.txt) is on the light side, and the code is on the heavy side. Don't get me wrong, there's some great documentation out there, and many valiant efforts on the part of developers, but you just can't always depend on extensive documentation - especially when you're looking at a module that's not particularly mature.
Update: The ability to conduct these searches appears to be broken with the move from http://cvs.drupal.org to http://drupalcode.org.
Sometimes you want to measure how much you've contributed to Drupal.
Sometimes you want to measure someone else - perhaps you're considering hiring this person.
Try the following Google search (where "username" is the person's Drupal.org username):
site:cvs.drupal.org usernameThat's it. Not scientific or anything, but it'll let you get a handle on how often a person's username appears on http://cvs.drupal.org.