Passwords, user accounts, email verification. I have never liked requiring my website's visitors to register before they can leave a comment. There is a large segment of people that like to submit quality comments online, but they don't want to be required to leave their personal information there. So from the beginning, I have always allowed anonymous commenting by unregistered visitors and for the most part, they quality of the comments haven't suffered. However, allowing for anonymous comments also invited my site into a war against comment spam. My latest weapon to do the fighting for me in this war is Mollom.