Many of you may have tried Blog Commenting as a mode of linkbuilding. I wouldn't say it's the best or it's proven to be real good but i can surely say that it works.
There are tonnes of open-source platforms out there that are available for free using which we can create a self-hosted blog of our own.

I'll try and cover up Wordpress, Movable Type & Drupal in this Post/Thread.

What are Footprints?

Footprints basically are the imprints or traces of a platform that are left behind on each page created using it. Unless explicitly removed by the webmaster, every blog, cms & forum platform has a footprint on every page in the footer section. In simple terms, a wordpress footprint is a piece of text like "Powered By Wordpress" or something similar that is common on all pages created on a wordpress-run blog.

We can use these footprints to track down and find pages of any type on the web that we may require for any specific reason. Google is the main tool we'd use alongwith the advanced search parameters like 'site:', 'inurl:','intext:',etc...
We can also find .Edu & .Gov pages that have commenting enabled so that you can get some link juice if the link happens to be dofollow.
It is believed(though denied by Google) that .Edu, .Gov, .Mil and such high priority domains happen to pass more link juice than the normal TLDs like .com, .net, .org, etc...

Just a search as simple as 'site:.edu' can give you a list of all the indexed .Edu pages on the web. However the only way of finding out on which page you can have your link placed is using footprints.


Getting back to blog commenting, following are certain platforms that allow users to post comments on certain pages while also allowing you to share your link.



Wordpress

Used Widely & has the most number of indexed pages than any other platform.

Following are the footprints that can be used to find Wordpress Pages ::

site:.edu "powered by wordpress" ---- 494,000 results
site:.edu "Leave a Comment" "Name" "Website" ---- 3,520,000 results
site:.edu "Leave a Reply" "Name (required)" "Mail (will not be published) (required)" "Website" ---- 11,400,000 results (Recommended)
site:.gov "powered by wordpress" ---- 48,200 results
site:.gov "Leave a Comment" "Name" "Website" ---- 39,600 results
site:.gov "Leave a Reply" "Name (required)" "Mail (will not be published) (required)" "Website" ---- 81,600 results (Recommended)
These will give you the various wordpress pages, however it isn't necessary that all pages you receive will be from wordpress itself.
There will be many custom created platforms that have similar footprints.

You can find niche-specific pages by adding your keyword within double quotes, e.g.

site:.edu "Leave a Reply" "Name (required)" "Mail (will not be published) (required)" "Website" "My Keyword"
To find pages having your keyword in the URL :
site:.edu "Leave a Reply" "Name (required)" "Mail (will not be published) (required)" "Website" inurl:"My Keyword"
Below is a screenshot of a typical Wordpress Comment section :


Pros And Cons Of Wordpress :
1) Links are Nofollow By Default.
2) Akismet can flag a legitimate comment as spam. Avoid using your personal e-mail address.
3) Registration to comment is not always required unless explicitly selected by the Webmaster.
4)Link Can be placed Within Comment text or in the ‘Website’ field with the anchor text in the ‘name’ field.
5) Comment Approval can be Auto or Moderated(Majority).

Movable type


Not as widely used as Wordpress but the userbase is still considerably high.

Footprints are as below :
"Powered by Movable Type" "My Keyword" ---- 26,300,000
"Powered by Movable Type" "Post A Comment" ---- 2,070,000 results
"Powered by Movable Type" "Leave A Comment" ---- 25,100,000 results
"Powered by Movable Type" "Name" "Email Address" "URL" ---- 3,620,000 results
"Powered by Movable Type" "Comments (You may use HTML tags for style)" ---- 2,060,000 results
For niche specific pages and for the keyword to be in the URL, use the same extra parameters in the search as given above in the 'Wordpress' section.
i.e. "My Keyword" & inurl:"My Keyword".

The Movable Type Comment section looks like :


Pros And Cons Of Movable Type :
1) Less pages than Wordpress, so less probability to find a niche specific page.
2) Nofollow by default.
3) Approval Policy - Auto or Moderated(Majority).
4) Link Can be placed Within Comment text or in the ‘Website’ field with the anchor text in the ‘name’ field.

Drupal

My Personal favorite.
Mainly used as a CMS and a multi-user blog.

Footprints as follows :
site:.edu "Login or register to post comments" "Powered by Drupal" ---- 375,000 results
site:.edu "Login or register to post comments" ---- 3,220,000 results
"Login or register to comment" "Powered By Drupal" ---- 957 results
site:.gov "Login or register to post comments" "Powered by Drupal" ---- 1,790 results
site:.gov "Login or register to post comments" ---- 165,000 results

A sample Drupal comment section looks like :



Pros And Cons Of Drupal :
1) Dofollow By Default
2) Link Needs to be placed within the comment section in HTML format.
3) Registration is required to be able to comment.
4) Comments are generally Autoapproved, i.e. no Moderation.
5) Low level of spam protection.

I would highly recommend using Drupal for blog commenting as a form of linkbuilding. Autoapproval & Dofollow by default being its best Advantages.

Wordpress, though nofollow by default, it has plugins that when installed by the webmaster, make links within comments as dofollow or provide some other Seo-related benefit. These plugins include KeywordLuv, CommentLuv, Nofollow Free, etc...
Free Blog Commenter is a free tool/scraper that can find keyword-specific dofollow wordpress pages. I use it at times and it works like a charm, what it makes use of ofcourse is Google's custom parameterized search alongwith the plugin footprints.

When you comment on a Blog just for the reason of getting a link, make sure you provide some valid, useful information that makes you placing that link of yours justified. Never place your link within the comment section in Wordpress or Movable type, make use of the 'Website' field.
As far as you do it right, blog commenting as a form of Seo is not considered as spamming.


Note :: Search Result stats are as of 30th August 2010, including omitted duplicate entries.