It appears something has changed on trunk as my test runner stopped working (on trunk, release is still fine) around the 5th May, I suspect I was doing something wrong.

user-config.jam contains:

using gcc : 4.8.0_c++11 : g++-4.8 : <cxxflags>-std=c++11 ;

Invocation of run.py:
./run.py --tag=trunk --runner="BP x86_64 C++11" --toolsets=gcc-4.8.0_c++11,clang-3.2_c++11_libc++ --bjam-options=-j7

bjam.log outputs:
/home/ben/development/boost/test/build/tools_bb/util/numbers.jam:22: in numbers.check from module numbers
error: 0_c++11 in 4 8 0_c++11
error: is not a number

Fair enough, seems I was abusing the version field (for both clang and gcc)

Is there a recommended way of creating a toolset with a name that has certain options defaulted, such as std=c++11?