Lots and lots of companies and government sites. Lots. And if you’re using a compiler or runtime of another language, such as Java, chances are good that it too is implemented in C++.
There are too many C++ users to effectively count them, but the number is in the millions. C++ is supported by all major vendors. The large number of developers (and therefore the large amount of available support infrastructure including vendors, tools, training, etc.) is one of several critical features of C++.
During 1980-1991, the number of users doubled every seven and a half months (see The Design and Evolution of C++). The current growth rate is steady and positive. IDC’s 2001 estimate of the number of C++ programmers was “about 3 million”; their 2004 number was “more than 3 million.” That seems plausible and indicates a continued growth. Especially since about 2010 there is a renewed growth in C++ as both mobile and datacenter applications value “performance per Watt” as a new mainstream metric.