I read on News.com that Google is promoting a new attribute for the html tag <A> for preventing comment spam.
Example: Visit my <a href=”http://www.example.com/” rel="nofollow">discount pharmaceuticals</a> site.
Google will not follow such a link (because of the nofollow attribute) and hence the linked site will not get Pagerank. This should give less incentives to blogspammers in automatically commenting your blog with spam messagges. I think it will not work but this is just a try for tacking spam and hence worthwhile.
What is more interesting is the “decentralized” evolution of (HTML) language. The new attribute is just a proposal from Google to extend a standard language but Google has a so high reputation that many people will follow this suggestion and this means Google has the power to change HTML language. Technorati did something similar proposing rel="tag" just few days ago. Technorati proposed also VoteLink with rel="vote-for" and rel="vote-against" and XFN with rel="friend met" and others relationships-related tags.
Actually everyone can propose a change in HTML language (or whatever language/protocol) but it is of course difficult to have it accepted by a significant number of players/content creators.
It will also be interesting to see if this language evolution will produce different linking behaviours.