Recently, on the blog

Answer: When they're an overseas design sweatshop using dodgy SEO tactics.

I'm used to getting comment-spam on my blogs. Disqus is cleans out most of it automatically, but a few make it through to publication. Fortunately, Disqus sends out notifications on new comments, so I'm able to manually filter out anything that doesn't seem genuine.

What is comment spam?

Comment spam is used by dodgy SEO businesses trying to build backlinks for themselves or their clients. The idea is that you choose a blog that's relevant to the search terms you want to build PageRank for and insert a comment (genuine interaction seems to be unneccessary) that has a backlink to your site. 

While this can build pagerank on the site you've linked to, it only works if the site you're spamming has a higher pagerank than your own and is relevant to the kind of keywords you hope people will use to find your own site.

It also won't help you if you get branded as a spammer by doing so.

Validating a website has become standard practice among designers over the last few years. As a site nears completion, the designer tests the site against the W3C Validator service to ensure that the code meets the standards, allowing them to proudly display a badge declaring their competency.

I have no real problem with this, except insofar as it provides no value (except to the designer's ego!) to show this badge.

The real problem lies with the claim that validation is inherently valuable as an SEO tactic. Sites like Google, Amazon and a plethora of other high-ranking sites stand as proof positive that validation alone will not ensure your site ranks highly.

So why is validation touted as an SEO technique?