From Newlaunches.com:

The Google index started with 26 million pages in 1998, shot to a billion pages in 2000 and now it is has hit a new milestone: 1 trillion (as in 1,000,000,000,000) unique url's. Google claims not to index every one of the trillion pages as indexing can be expensive as many of them are similar to each other, or represent auto-generated content. The way Google indexes has evolved it now indexes blogs and other rapidly changing websites every 15 minutes. Michael Arrington of Techcrunch hints at something big coming up next week which may challenge Google position of having the most comprehensive index of any search engine.

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