I have definitely seen an increase in rank with each backlink I drop. Blog commenting is all about Karma. If you post 3 words with a spammy keyword for your anchor text, then don't be mad if your comment gets deleted. Now if you run a stand up website, even if it's a business and shameless self promotion, at least lend something to the convo. Most blog owners don't mind giving you a backlink if your a real person with something to say. As a website developer and blog owner myself, I believe spam bots need to be outlawed, lol