Extremely helpful. Just don't use your blogger id or any other open id, as it will not give any effect.
Depends actually. Eventually, you get what you pay for. More than the niche, it makes sense to look into other factors such as the age of the post, number of external links, moderation, quality of other commenting links(you do not want your site to share the same page with viagra, porn links.. ) and there is a very thing line between blog commenting success and abysmal failure that you have to tread on. MECHANIX
it works better if you comment on blogs withing your same niche but it sure works more or less. i have seen people reporting good success from blog commenting
Of course, especially on Do-Follow Comments What's better than a free juicy back link from a indexed page?
It's an exceptional way to secure links becasue if you do it manually you can choose among hundreds of very relevent blogs on many different ips and geographical locations. Google will be salivating at the link food with its spiders.
Another thing you should keep in mind while posting them is checking up other pages of the blog. If they have Viagra, Cialis or Porn links, then there is a high chance that the page you comment on will eventually acquire those. Being associated with those links can do more harm than good.
Very Helpful! Results in back links. Even if it no follow links. Plus the traffic you get from people reading your comments then maybe clicking your link to see what your site is about. So it helps with traffic, back link building anf maybe even comments on your blog if you have one.
As noted, if the blog is DoFollow, it will help for SEO. If it is NoFollow, then it might help with some traffic and getting your site out there, but will not help much in terms of Google (other SEs still might follow it some).
I think they are really helpful bot for SEO and traffic, so keep your fingers over the keybord writing to comments on blogs