I have built gcc 4.7.2 and run the array tests. I see the failure that you reported. I also see a gcc crash in the test "array_constexpr":
darwin.compile.c++ ../../../bin.v2/libs/array/test/array_constexpr.test/darwin-11/debug/array_constexpr.o array_constexpr.cpp: In member function 'void test_main::test_method()': array_constexpr.cpp:32:36: in constexpr expansion of 'arr.boost::array<T, N>::at<int, 10ul>(3ul)' array_constexpr.cpp:32:36: internal compiler error: in adjust_temp_type, at cp/semantics.c:6400 Please submit a full bug report, with preprocessed source if appropriate. See <http://gcc.gnu.org/bugs.html> for instructions.
More as I find it out. ;-)
Just so you know, this is causing all the C++0x mode Boost.Math tests to fail currently. Tricky one to solve though :-( John.