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.
AFAIK targeting is done only for language, location... and previous searches only if you allow Google to keep your search history.