It's funny you mention JSON parsers and Boost in particular. The Boost JSON parser is an abomination. It's written as a parser generator in template code, so any file which includes it gets about 10 seconds of compile time just for that. It also blatantly violates the JSON spec and gives little to nothing in terms of parse error messages. Oh and until recently it was neither thread safe nor reentrant (you could not parse two JSON files on two different threads in the same process because it used shared global state for all parsing).

I remain baffled that anyone uses boost for anything in production.