I'm not sure whether or not those links will be do follow links but google considers many of those comment posting links to be spam.
Most of these sites are NoFollow anyway, or they strip the links that you include away. However, there are many magazines out there that have dofollow comments enabled as part of their CMS systems they use. I just found around a dozen such sites that are PR6/PR5, some with well indexed pages that allow for dofollow comments. Many of these were relevant to the content that I was promoting and I have seen some traffic come from these sites.
I'd say that all the major ones are nofollow. However, they do provide traffic, particularly if you can write something intelligent and/or controversial. But like most news it's tomorrow's chip papers, figuratively speaking: the traffic doesn't last.
Posting on popular pages is useless because they are all nofollow. Google does not give you credit for those, so it's just a simple waste of time.
How do you know this? If comments are allowed, why would they automatically be considered spam? Do you have solid evidence of this?
Comments are always useful for link builders, especially on high PR site but comment should be more related to the content or post. i am agree with all of you that commenting is a useful tool for link building. one thing more it also help in page indexing if your site is not index. thanks for the information
I don't quite agree with you. If your comment is genuine, and pertains to the topic at hand, why would it be considered spam by Google?
do you say that google can identify comment links from other types of links and consider them spam!!!
those sites are very likely to be nofollow.. so there isnt much point in building backlinks with them
Even its a do-follow and have a high PR, if its not related to your website, i thinks its not so good at all.
Using Firefox you can right click a link look at properties and quicly see if the link shows rel nofollow