I agree, Simon pretty much summed it up pretty well.  I was thinking the question was asking "Is it still a useful way to get a backlink?" which it is but only if done right and not a one time action.  We're obviously on the same page though.  Thanks for the clarity in your answer.

I have to disagree with William Lau.

I think that blog commenting has changed a bit.  It think it is still relevant.  I prefer the term Comment Marketing and Link Earning because that is my goal, to market my site and earn links.  Here is how I do it now.

I find blogs that are relevant to my industry and of people who I really want to have link to me (authority figures).  I follow their blogs and comment regularly on them.  My goal is to build up enough trust and awareness of what I am all about.  I have two goals here.  1) if my comments are good then people will want to learn more about me and click on my profile/link to go to my site (not so much for SEO purposes but for site traffice) ( I don't care if I'm number one if no one goes to my site.  Traffic is important to me.  Even better, relevant traffic.) and 2) I want to be able to eventually earn the right to become a guest blogger or have that person read about me and link to my site because of it's good content.

I think the idea of posting a comment for the sake of posting a comment is pointless.  SEO is changing (for the better) and SEO now should stand for Search EXPERIENCE Optimization and not Search Engine Optimization.  Comment Marketing is relevant if you use it to help build traffic and not to earn "traditional SEO links".