BCB6 Patch 4 was not tested against this release, and several version checks only test for __BORLANDC__ <= 0x561. SP4 raises this to 0x564, and it may be necessary to patch some files by hand. A quick search on 561 turns up quite a few headers in the MPL and Spirit.
By default the FileSystem? library is built as single-threaded. VCL applications will require a multithreaded build though. This typically will not be picked up at compile/link time, but might result in unexplained deadlocks at run-time.
Despite failing two of the 5 tests the boost::array library is quite usuable under BCB (tested with 5 and 6) The problem is purely with a specific form of initialisation syntax. If you look at the two failing examples and change std::string to char* the tests will pass. Alternatively, you can stay with std::string but need to populate the array manually, rather than through the initialiser syntax. The problem only surfaces when trying to create arrays of non-POD objects.