Although it's difficult to say if there is any direct SEO benefit from nofollow blog comment links (Twitter links are nofollow but are being seen increasingly as a positive SEO factor but that's a completely different conversation I guess), there are many other advantages of contributing something relevant to a authors blog post.

If you take the time to offer value to the visitors of a blog post with something information or thought provoking then it will most likely be approved and potentially send people to your site too (through your profile link). Once they are on your site you have a captive audience who could share your links if they think it's of value to their contacts.

Blog commenting for SEO sake is a really tired practice and something which is more of a nuisance and an insult to bloggers who spend time constructing something of value for others to try to spam and leach from.

Assuming you are commenting because you think you can offer something to the post then it can offer many advantages in my opinion.

Its still a link and is worth it.

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A Backlink is a Backlink, so yes, it is worth getting any kind of backlinks, there got to be some worth for it whether do follow or no follow, in any case to show link diversity it is always and anytime nice to have all types of backlinks

At the very least it'll improve your link diversity. (Helps you look a bit more natural.) So I wouldn't turn down a backlink even if it's nofollow.

Hi, Yes comment blogs work.

I don't have a problem with no follow backlinks as it proivides diversity in my backlinks. I think google likes this.

Nofollow links actually have a stronger correlation with rankings than dofollow links, although that might just be because sites with a lot of nofollow links have a more balanced link portfolio. Still, you definitely want some.

Can you choose between the NoFollow and DoFollow link? Than always go for the DoFollow.

Since that really isn't all that easy for most of us, just get the link as long as the page isn't spammed to all hell and that you can add some truly valuable feedback to the blog.

Don't go on a spamming rampage though, it really won't benefit you in the long run.

Nofollow links certainly doesn't have the same importance as dofollow links have, but both links have importance in serch engine's eye.
Secondly blog comments are good way of promotion and getting quick targetted traffic.

Why wouldn't there be any benefit? If you comment on a site that is relevant to yours, aren't you 1) building links from relevant sites and 2) getting traffic from people/potential customers in the same or related market? I don't know why people worry so much about follow/nofollow?