I think that Bitcoin is as big as I think it is - a $2B economy with >10K businesses and hundreds of thousands of users.
Based on data from
http://www.similarweb.com/website/bitcointalk.org, it looks like the forum gets about 1M pageviews per day.
Google:
how do I buy
look at what comes up
You do know that Google search results and autocomplete are targeted? If you look at Bitcoin all day, it will give you Bitcoin-related results... It has little to do with Bitcoin's popularity.