I'm guessing that the latest announcement from Google, amongst others, to try and prevent comment spam doesn't have the blessings of the W3C. The question you have to ask yourself at that point is of course, is that a bad thing?
HTML was designed to be extensible, and browsers were designed to ignore markup they didn't understand and render the pages on a "best efforts" basis. Additionally the HTML standards change and grow constanty, and as new tags are added, older features are eventually deprecated.
But the fact we can talk to each other at all over the Internet is due to the existance of standards. Just because HTML is a high level standard and isn't crucial to the nuts and bolts underlying the network, and also the software that deals in it is now so ubiquitous, it doesn't mean that the standards process itself is irrelevant.
While I welcome any move to try and do away with comment spam , I'm not sure I approve of the way they've approached things. Don't standards mean anything anymore?
Update: Should my face be red or not? I haven't decided yet. While nofollow isn't one of the standard link types, other additional types that are not described in the specification are apparently allowed. However if you use non standard types, you should use a profile to cite the conventions you used to define the link type. So long as the right information goes into the HEAD element, then everything is above board. Err, want to guess how many people will do this correctly?