Solved and swept on 16 Jan 2015. The private key for this 31-bit puzzle was found inside [2^30, 2^31) and the balance was moved out.
A solved puzzle is a benchmark. Running a cracker against it should recover the real private key, which is how you tell genuine code from a toy. Puzzle #31 needs about 2^29 key tests on average, within reach of a laptop in minutes.