The problem here is that there is no machine-readable disclosure for paid links. Matt suggests that there a “ton” of ways, but none of these ways mean “this link is paid”

Nofollow, in particular, does not mean “this link is paid.” What Google is really asking webmasters to do is “filter the paid links for us.”

Given that Google’s remedy for sites that fail to do this for them is to remove that site’s ability to “recommend” another site by passing PageRank and link reputation, those selling advertising should at least consider going along with nofollow.

It’s ludicrous to attempt to the “machine readable disclosure” expectation to buyers of advertising. Even threatening to penalize advertisers for legally purchasing advertising strikes me as more than a little bit likely to result in legal problems for Google.

At least in the USA, it seems clear enough that the law requires human-readable disclosure of paid links. That’s something a lot of sites need to catch up to, but search engines need to get smarter about automated discovery instead of relying on pressure tactics.

True, but that’s why the “If-Modified-Since” HTTP request header exists. The SERPs for any query consist of fresh results, i.e. results that are likely to still exist and be what the robot saw. That’s not to say that the results need to be recently created - just recently verified.

> Maybe, rather than freshness, it is better thought of as … “document accuracy”, i.e. the likelihood that the data stored for a document is accurate,

That’s exactly what’s at issue.

Some content will not to change much. Take the W3C HTML stanadards:
http://www.w3.org/TR/html401/

Given that some content doesn’t change, I would argue that it is prudent to not bother downloading such pages very often. In terms of bandwidth and useful utilisation of a parser (which, with ever increasing elements to uncover, is probably taking more CPU cycles than ever), the resources spent grabbing an unchanging page are better spent grabbing either new content for the index, or refreshing content that changes regularly, like the front page of Digg or news sites.

Reconciling an algorithm that optimises the utilisation of crawl resources, that likely discriminates against primary sources that never change, with a usage of “last crawled date” in rankings would be problematic, especially when the search clearly wants the primary source.

Sure, you could make the last crawl date for such pages constantly NOW, but that makes the ability to optimise crawling schedules (which would be as close to 1 second after publishing as possible :)) potentially harmful to results. Optimising in two direction (crawl effieciency and relevance) is terribly difficult.

Maybe, rather than freshness, it is better thought of as “staleness” or “document accuracy”, i.e. the likelihood that the data stored for a document is accurate, with staleness the moment at which trust in the accuracy of the indexed copy moves from accurate reflection to not an accurate reflection.

Freshness, per se, doesn’t really matter, but accuracy does. Such a measure would aslo alow different documents to loss the trust in teh acuracy of the indexed copy at different rates (a news site’s home page, for example, would likely be innaccurate after 10-15 minutes; a side with every legal judgement likely has a lot longer decay cycle).