I've added a
do follow blog search tool to my website which I've found useful. I have yet to fully check all url's that it searches so some may have enabled the rel=nofollow attribute on comments.
When targeting dofollow blogs I'd always advise targeting relevantly themed blogs with good quality comment posts. Don't just add your name as Cheap Car Insurance followed by the comment Nice post. If blog owners have removed the nofollow attribute it may be that they want to reward visitors who take the time to leave good quality comments. Abusing the system will only result in your comment being deleted or the nofollow being reinstated.