Blogs provide you backlinks.. If your links are in comment section,this is just a backlink because most of the time it is nofollow. No effect on pr value.. However if your link is placed in the blog itself,this is backling and also dofollow. Blogs are effective indeed in communicate.
I find setting up your blog as "dofollow" is a great way to bring in traffic and get people to get involved on your blog, it's like the nectar that brings in the bees to pollinate your adsense clicks!