Google announced their latest big change to the search results November 3 – fresher, more recent results. The change comes with the help of Caffeine web indexing system which allows Google to crawl and index the web for fresh content quickly on an enormous scale.

This significant improvement to Google's ranking algorithm impacts roughly 35 percent of searches and better determines when to give more up-to-date relevant results for varying degrees of freshness.

• Recent events or hot topics: For recent events or hot topics that begin trending on the web, you want to find the latest information immediately
• Regularly recurring events: Some events take place on a regularly recurring basis, such as annual conferences or recur more frequently. Without specifying with your keywords, it’s implied that you expect to see the most recent event, and not one from 50 years ago
• Frequent updates: There are also searches for information that changes often, but isn’t really a hot topic or a recurring event.

(source)

To clarify, when we say this algorithm impacted 35% of searches, we mean at least one result on the page was affected, as opposed to when we've said noticeably impacted in the past, which means changes that are significant enough that an average user would notice. Using that same scale, this change noticeably impacts 6 - 10% of searches, depending on the language and domain you're searching on.