Yep I remember now that you had talked about that already last time we mentioned our work, I completely forgot to look at Boost.Math bindings since then. However I don't find any real documentation about what it is exactly (rationale + use case(s)). If the purpose is the same as our work, there would be no problem to migrate our work into your (add CLN for instance).
Browse the topics starting here: http://www.boost.org/doc/libs/1_40_0/libs/math/doc/sf_and_dist/html/math_too..., the bindings add just enough syntactic sugar to make the two arbitrary precision libraries so far supported conform to our concept requirements (http://www.boost.org/doc/libs/1_40_0/libs/math/doc/sf_and_dist/html/math_too...). In other words to make them look "just like a regular std number type". Both NTL::RR and mpfr get pretty close to this already BTW, there were just a few features and Boost.Math specific traits/helper functions that were missing. Cheers, John.