Matt Cutts and Amit Singhal write for Google's official blot about what the latest algorithm change does:
This update is designed to reduce rankings for low-quality sites-sites which are low-value add for users, copy content from other websites or sites that are just not very useful. At the same time, it will provide better rankings for high-quality sites-sites with original content and information such as research, in-depth reports, thoughtful analysis and so on.
So you can take it from the inverse of that "high-quality site" description, as Search Engine Land does, that sites serving only to quickly put up posts related to high-ranking search terms won't be doing quite so well. And Google is pleased at the correlation between their DIY Chrome blocker and what shook loose from this search change:
... (W)e did compare the (Chrome) Blocklist data we gathered with the sites identified by our algorithm, and we were very pleased that the preferences our users expressed by using the extension are well represented. If you take the top several dozen or so most-blocked domains from the Chrome extension, then this algorithmic change addresses 84% of them, which is strong independent confirmation of the user benefits.
Like everything Google, it's a rolling change — some users may not see it right away, and it's US-only at the start. Still, if you're searching Google and see some notable improvements, tell us about them in the comments.
Finding more high-quality sites in search [Official Google Blog]