RSS Feeds and Real Time Crawling
A while back an update went live that, with some caveats, changes the time it takes for an update on a website to reflect in the search engine index from up to 2 months to 1-2 days. Conditions being if the website has an RSS or Atom feed.
The big crawl job takes about two months, and is run partition by partition, meaning there's typically a slice of the index that is two months stale at any given point in time.