Just another thought on dofollow: There's still a real buzz about it. And there are a lot of lists being posted on various blogs and forums. There are also quite a few people selling large lists of them!
People are clearly hungry for this information. But it's very easy to bite off more than you can chew.
I mean, if you buy a list of thousands of dofollow blogs, this may make you feel like you've done something really useful. But how many of those will you ever even look at, let alone comment on?
Of course you should keep an eye out for these blogs. But the main thing is to just look for informative blogs in your niche. Then the commenting will flow naturally, and you'll do more of it. Dofollow links will come as a result, either directly or indirectly.