Black Hat SEO can be a great thing!
Yeah, I know, as an SEO Company I'm not supposed to say that, but it's a great way to get noticed!
Depending on your product and the needs, you could market a "quad-helicopter" toy for Christmas for example. So the month before christmas, setup a website (doesn't matter the name), market the crap out of it using underhanded techniques, sell a bunch of toys, let the site die.
This works - much like SPAM works. You don't care about the site, Google de-indexes it, and you make over with your money to build a new website.
On the other hand, if you're a business, and you plan to be around, if you go into BlackHat SEO you'll hurt your business in the long run. When you get caught, and you will, your website could be removed from the search engine listings and thus kill your "organic" traffic.
Blackhat SEO does have it's place, and it is 100% a violation of Google's rules. If you participate in it, be prepared to be slapped.
*** Our company does not participate in BlackHat SEO techniques - we only work with Real Businesses. Any request for Black Hat, or even Gray Hat SEO, is immediately rejected.