Cheetah is stable, production quality, post-beta code. Cheetah's syntax, semantics and performance have been generally stable since a performance overhaul in mid 2001. Most of the changes since October 2001 have been in response to specific requests by production sites, things they need that we hadn't considered.
As of summer 2003, we are putting in the final touches before the 1.0 release.
The TODO and BUGS files in the Cheetah distribution show what we're working on now or planning to work on. There's also a ToDo page on the wiki (see below), which is updated less often. The WishList page on the wiki shows requested features we're considering but haven't commited to.