[boost] Building software with Boost

Hi, There are two questions for which I have found no answers: 1. When exactly are -mt (multithreaded) versions of the libraries needed? 2. Boost.System was added in 1.35 and apparently some of the old libraries also depend on it in new Boost versions. Are the inter-library dependencies of Boost actually documented somewhere, or does one need to guess? I need this information in order to write a new FindBoost script for CMake.