Please remember boost is just a set of libraries which can be used to improve productivity (stop reinventing the wheel).
They are, by all accounts, well written and use techniques that you might not (i.e. defintely won't) think up by yourself. If your intention is to look through the source to learn advanced c++ techniques then knock yourself out but I think I'd buy a good book instead.
On the other hand, if you just want to use some library functions to improve your productivity consider your options. What are you developing and so what sort of libraries do you need?
Our company has cross platform products that use boost extensively but we also have windows only products that use some boost but, for the most part, rely on microsoft's libraries. MS libraries are good quality and have (imo) excellent documentation (part of MS success lies in making windows as easy to program as possible for third party developers). I mention MS specifically as they offer a broad range of libraries for many purposes like boost. We also use numerous other more focused 3rd party libraries (i.e. libraries that provide functionality in one area such as cryptography).