If that was a serious question, places that do developer tools and programming languages for a living (at least MSFT, I assume others as well) pay ridiculous amounts of money to independent third-party companies that specialize in gathering this kind of data. The raw data was then kept fairly private (marketing + upper mgmt only), but the rank and file would see some of it occasionally when things such as trends on the number of VBA or VB5 or VC++ programmers appeared in slide decks talking about the direction for upcoming versions of the product.

Having working with the raw data, it was pretty fantastic. Segemented by industry/business size, handled issues with multiple programming languages or companies where one section used one language and another used other ones, etc. We even knew which tools and add-ons were used for which languages and which compiler on each platform (i.e. how many commercial shops using C++ targeting linux are using gcc vs. icc?).

But that data was also stunningly expensive. My marketing friends tell me that accurate market data always is.