Is it still useful to use black hat and borderline black hat techniques for SEO purposes?

[Anita]

Google's anti-spam team are constantly revising the algorithm to filter out web spam... from links created using automated software like blog comments etc, through to hidden text... now days it even goes so far as to "read" your page to check it makes sense and is contextual and so keyword stuffing get detected pretty quick.

What is important to note however is not only will these type of bad links and practices no longer help your rankling, it can actually drop you in the rankings, and in some case get your site sand-boxed (essentially banned).

My advice, steer clear of ALL shady techniques, even if they are not detected now, chances are an update in the future will cost you dearly as recovering from a sanction is a costly process.

Some good tips in the article below, hope this helps..