I can't compare to other implementations, but you may find my articles
on pyjaco helpful in terms of measuring maturity:
http://archlinux.me/dusty/?s=pyjaco
I don't know how much of it is me and how much is pyjaco, but I find it
a bit unwieldy to work with at this point. There is quite a lot of
change going on in the codebase, all for the better, but it may affect
short term stability a lot.
I think the biggest limitation of pyjaco is the need to flag javascript
variables (e.g. jQuery) separately whenever you manipulate them. As a
coder, this leaves a lot of state that needs to be managed. I guess the
other possible limitation is that pyjaco ships a standard library. It's
not terribly big, but it does add some weight to javascript files. There
is discussion on ways to shrink the shipped library file such that only
those functions that are used during compilation are actually accessed,
but nothing has been done yet.
Take pyjaco out for a spin and let us know what you think. :-)
Cheers,
Dusty