So much NONSENSE about link building and backlinks...

blog commenting CAN (and is) good but it takes a very long time, even when you use tools like scrapebox and filter 100k+ blogs. There are very, very little dofollow. Furthermore there is also a factor "link strength"....that is you would want to have a link with very few outbound links because many OBL decrease link strength.
I can run 100k blogs and then come out with maybe 5 PR6 blogs and a little more PR5 - but then its not even a given that your comment will ever get approved since so many blogs are not moderated or simply the admin doesn't bother to check comments and approve them.

As for .edu .org..people tell all the time they are "trusted"....but there is an easy NUMBER which reflects the trust, this is the PAGE RANK. Because the page rank is a direct indication how many sites link to the site, no matter what extension, .gov, .edu doesnt really matter. Unless i have hard proof that .edu/.gov is something special i simply dont believe it You would have to ask Google themselves and i am almost certain they would say it doesnt matter.