I've been reading recently about Stackless Python and it seems to have many advantages compared with vanilla cPython. It has all those cool features like infinite recursion, microthreads, continuations, etc. and at the same time is faster than cPython (around 10%, if the Python wiki is to be believed) and compatible with it (at least versions 2.5, 2.6 and 3.0).
All these looks almost too good to be true. However, TANSTAAFL, I don't see much enthusiasm for Stackless among the Python community, and PEP 219 has never come into realization. Why is that? What are the drawbacks of Stackless? What skeletons are hidden in Stackless' closet?
(I know Stackless doesn't offer real concurrency, just an easier way of programming in the concurrent way. It doesn't really bother me.)