CPython 2.5. Works fine. Can be sped up with Cython or Psyco (x86 only).
CPython 2.6. Works fine. Can be sped up with Cython or Psyco (x86 only).
CPython 2.7. Works fine. Can be sped up with Cython.
CPython 3.0. Works fine. Can be sped up with Cython.
CPython 3.1. Works fine. Can be sped up with Cython.
CPython 3.2. Works fine. Can be sped up with Cython.
Pypy 1.5. Usually works, but sometimes leaks memory.
Pypy 1.6. Contained an os.stat()-related bug that causes tracebacks.
Pypy 1.7. Works well.
Pypy 1.8. Works well. Very fast - faster than the Cython's (!).
Jython 2.5.2. Does not work.
Jython 2.5.3 -r 7288 no longer works; it does not update timestamps correctly.
Jython 2.5.3b1 mostly works, but skips backing up device files. Should be able to restore device files though. It also cannot detect symlink races during backups, which has security implications.
Cygwin CPython 2.x. Works fine.
Be sure to check out the performance comparison too.