My mate Owen, over at the only network, Has a post about Analyze Backlinks

There is website that will tell you all the sites that are linking to you. It is well worth a visit as it will allow you to understand how effective your commenting is on other users blog. Key to gaining a good page rank is insuring that authority bloggers link back to. So commenting really is important for your blog. The rule of thumb here is the more links the higher the page rank. So get reading and positively participating.