Google doesn't show the number of pages in the index on its homepage, but a good way to find it is to search for "* *". The resulting number is 25,270,000,000. Google says their index is more than 3 times larger than any other search engine. But what kind of pages are included in this huge index? Let's see:
Search for [site:t1ps2see.com]: 2,460,000,000 results and every page is a search result from a spam site.
Search for [site:eiqz2q.org]: 5,100,000,000 results that redirect to the same t1ps2see.com spam site.
Here's Alexa traffic:
And the list of spam sites is really long. So that means Google has upgraded its index with spam sites.
Note: Yahoo and MSN have very few pages from the sites mentioned (MSN: 59 results, Yahoo: 11,800 results for [site:eiqz2q.org]).
Also read:
Examples of queries for which these sites rank well
Search Google searches (where you can see how Google indexes search results from Blog Search, Google Maps or Google Books).