This blog didn't used to get very many comments. I have been using dofollow for a while but never got around to putting a banner up that stating that fact. This puts me in good company. Why not give back to people who comment on your blog by giving them a good link back to their site instead of basically slapping them in their face for their comment. "Thanks for the comment, but I am going to treat you like a spammer and link back to your site with a nofollow tag." The point of nofollow was to prevent spammers from gaining links from blogs.
Even worse, there are bloggers out there who fly the dofollow flag and are on the dofollow lists, but if you look at their source code, they are using nofollow. They are dofollow liars.
I go back to Andy Beard for a list of do-follow plugins for Wordpress.
This next one is relatively new and adds a new twist. Not only does the commenter get a link back to their site but also to their last post. Talk about link love. It's link love with anchor text. I am all for ranking #1 in Google for my name. But ranking for other terms help also.
A few dofollow lists that you can submit your blog to once you install the plugin.
This first one is highly recommended. Nickoo also has a variety of badges to choose from so you can tell your readers you appreciate their comments.