As they explain it:
We heard what people were asking for so we did a little homework and are now happy to introduce the 'robots-nocontent' tag.
This tag is really about our crawler focusing on the main content of your page and targeting the right pages on your site for specific search queries.
To do this, webmasters can now mark parts of a page with a 'robots-nocontent' tag which will indicate to our crawler what parts of a page are unrelated to the main content and are only useful for visitors. We won't use the terms contained in these special tagged sections as information for finding the page or for the abstract in the search results.
There is also a help page.
So, let's have it. What do you think? I'm still not convinced - I need to think a bit more about this...