The head of Google’s web spam team Matt Cutts announced the update today on Twitter and called it “minor,” saying it noticeably affects 0.7 percent of English-language queries:
Minor weather report: Update of goo.gl/OpIDL launching today. ~0.7% of English queries noticeably affected.
The link in Cutts’ tweet points to Google’s original post about the Page Layout algorithm from January, which explains the algo thusly:
We’ve heard complaints from users that if they click on a result and it’s difficult to find the actual content, they aren’t happy with the experience. Rather than scrolling down the page past a slew of ads, users want to see content right away. So sites that don’t have much content “above-the-fold” can be affected by this change. If you click on a website and the part of the website you see first either doesn’t have a lot of visible content above-the-fold or dedicates a large fraction of the site’s initial screen real estate to ads, that’s not a very good user experience. Such sites may not rank as highly going forward.
Google has promised more alerts for webmasters about its algorithm changes, and that’s certainly playing out over these past two weeks.