Jonathan Ledger has recently posted a new case study to evaulate whether obtaining links from Blog Comments is valuable or not.  I think his case study will be VERY successful!  And I look forward to reading his results.

Let's take a brief look at his case study.  Jonathan has built an adsense site with 11 unique articles.  To promote the site, he is going to post 600 comments on blogs that do not (*DO NOT*) use the "no follow" attribute.   The goal of the case study is to learn whether links obtained through comments posted on blogs have a positive impact on search engine rankings.

For example, my blogs (including this one) allow you to earn a link 
back to your site simply by posting good and valuable content in 
your comments. 

More on Jonathan Ledger's Case Study on using Links from Blog Comments