You can see the latest review of Google based on Algorithm. Here Google’s Matt Cutts video on YouTube which was posted answering a question, “In 2009, how many search algorithm changes were done till date? Is content still the king or something else (structure) has taken over? Answering the question, Mr. Matt said that Google hardly does a change each day to the search algorithm. Even they don’t release those changes every day instead release them in batches. Overall, what he feels to an average at least one change everyday to the algorithm. He believed that in 2009, they might have had between 350 to 400 or more changes to the search algorithm.
Few months back we read a wired story on Google’s algorithm where Udi Manber, Google’s head of search quoted that Google has launched 550 “improvements” to the search algorithm last year itself. What I feel that Mr. Matt Cutts was a little bit conservative to his calculation.