There was a time, when you had to wait for days (if not weeks) to see your content indexed by Google. Now a days, many web pages are indexed in 5-10 minutes. At least this is what’s happening to many blog homepages, which are updated in almost real time. Here you can see the homepage of a PageRank 4 blog:
and here's the proof that the blog post that was created 11 minutes earlier (the result is from Google Blog Search):
Google, Search, Search Engine, Web search, Ping, Index, Indexing, Web Indexing, Site Indexing, Blog Indexing, Real-time indexing
Google could use the ping feature of the blog search engine to get notifications when a site is updated. This doesn't work for all the blogs, so there may still be a prioritization algorithm.