DoFollow Blogs
Many people expect any blog they comment to give them a high-pr back link. The truth is, not all blogs have DoFollow activated, and that means that the link back won’t do anything for your page rank. You can find a directory of blogs that have DoFollow enabled Here. As long as the blog you’re posting on has DoFollow enabled, your link will be tracked by google, and will help to boost your SEO ratings.
There is a mozilla firefox plugin called Searchstatus which allows you to see if a blog is ‘dofollow‘ or ‘nofollow‘. The search status plugin shows much more than just if the blog you’re reading is ‘dofollow’ or ‘nofollow’. The plugin also shows the pagerank, meta tags, link status, whois, and other stuff.
The most important feature of Search Status, is that it highlights the nofollow links in light bright pink. If the blog is DoFollow, the links won’t be highlighted.
I always leave my plugin on, because if I find any blogs that have Dofollow turned on, I can leave a comment and get a useful backlink or two. Most popular blogs have DoFollow enabled because they’ve realized the importance to other bloggers.
To Make Your Blog DoFollow:
Making your blog a DoFollow blog is probably the easiest thing you could do on your blog. All you have to do is go to semiologic and download the plugin. Once you have it downloaded you just upload it to your blog like any other and activate it from the admin control panel.
Now your links will be worth something to other bloggers! 
In case anyone was wondering, I have DoFollow enabled as well.
Tags: backlinks, blog, blogging, building, dofollow, links, pagerank, PR, seo