A long awaited announcement was finally made Saturday by the PyPy team: PyPy-STM has reached a reasonable level of maturity and usefulness to begin comparison to PyPy and cPython. We can consider the first (C-based) GIL-less Python (disregarding that old "no GIL" patch from years ago which went nowhere).
The implications are important: Armin and team have proven that Software Transactional Memory is a viable approach to GIL-less multi-threaded Python. They are now ready to move to the second phase of the project, namely improving things to the point that there are no caveats to the statement "PyPy-TM can run existing multi-threaded Python code without a GIL and achieve reasonable speed-ups".
As someone who has followed GIL-related work for years (albeit from the sidelines) I can't understate how excited I am. Though Python continues to enjoy a reasonably high rate of adoption (I assume) across a number of disciplines, the GIL always made taking full advantage of today's multi-core hardware difficult at best. In a GIL-only world, Python may be discarded for similar languages that do not share the same drawback, especially as they mature.
Today's announcement, however, has made clear a road ahead for Python. If Armin and company are able to complete the second phase of the project (scheduled to last up to two years), I can imagine a world where PyPy becomes the reference implementation of Python. As crazy a statement as that sounds, that's how important I believe solving this problem is.
In general terms, today's announcement was a win for developer ingenuity and perseverance. Work on the STM branch began years ago, and there were a number of false starts. The team kept at it, though, and showed the rest of us that the hard problems are worth working on, assuming enough dedication (and not a little bit of intelligence and skill!). It's a win for those operating on the fringes of their fields, on the problem that few discuss and less try to solve. Most importantly, it's a win for the Python community at large.
Good luck to Armin and Remi (who are both committed to phase two assuming there is funding), as well as all who join them and contribute development time. I, for one, will be donating to support their worthy research.