Solved and swept on 15 Jan 2015. The private key for this 21-bit puzzle was found inside [2^20, 2^21) 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 #21 needs about 2^19 key tests on average, which the in-browser engine on this site finishes in seconds.