Up to date figures about the of Twitter as a search engine have shown a growth of 33 % since April. One have to contemplate the time span, which again is a sign of very fast growth.
The figures have been introduced by Biz Stone, a founder of Twitter, during the Aspen Ideas Festival. In absolute numbers 800 million search queries are done daily opposed to 600 million in April, which now means 23 billion queries monthly. A comparison with other search engines is not easy (s. article), but by this numbers Twitter has already passed Bing and Yahoo with 4.1 and 9.4 monthly search queries.