As a WhiteHat SEO Person that makes 100% of my living from SEO, I wouldn't advise using Blackhat.
That being said, blackhat DOES WORK, and can be quite effective in different niches, especially "short run" type marketing/websites.
Much like SPAM, which we all hate, SPAM *DOES* work in certain niches. If it didn't work, nobody would spend their money doing it.
So, to re-cap. BlackHat does work - but as a WhiteHat SEO Person, I would never advise it to a client. We work with clients for years at a time, and BlackHat can't sustain a longterm relationship.