I have led or contributed to dozens of Open Source projects. And with one exception, all of my code has been Object Oriented. (That one exception is Drupal.) Java, Python, PHP, and even OO Perl... I'm a dyed-in-the-wool OO developer. So this may come as a shock to anyone who knows me, but I am about to make the argument that OO is bad for Drupal.
Trust me, this is not a high point in my development life. I feel like I'm telling my child that she should skip college; that such a level of sophistication is just not necessary in her life. And I guess in a way that is precisely what I am saying.