What exactly does a “Do-Follow” blog mean? It means that all URLs posted in the comments, or the comment author link is followed and indexed by Google. That creates an automatic backlink for you once you post a comment on any of the posts within this blog. A lot of blogs have “No Follow” tags, which means that posting your URL won’t give you any credit, as this is being “snubbed” by Google.
All my blogs are Do-Follow blogs, so feel free to leave your URL when you post comments. Just try not to be spammy and leave several comments for every post with tons of URLs. That is so not cool. :p