1 Trillion Unique URLs

In 2005, Yahoo! revealed that they have about 20 billion pages. Then Google also announced weeks later that they have 3 times bigger than any other search engine, referring to Yahoo’s earlier claim. That makes it 60 billions indexed pages.
Only 3 years later, that’s now, Google has actually increased that more than 16 times to 1 trillion. The problem though is that I think this type o approach might bump into problems in scaling one day. How many more data centers and hundreds of thousands of server will Google spend on to keep the index growing and make searching still lightning fast?