It is a BSD licensed product, making it easy for businesses to use and modify the code. The estimated number of downloads is eighteen million. It is used by many research groups, companies, and even by some governments. It is written in C++; however, it has a great templated interface that works extremely well with STL containers.
In conclusion, it is a really impressive library that I would not hesitate to recommend to any coder that knows what they are doing. It is a fantastic product that is continually growing.