I was going to mention Django but you beat me to it. Actually, my whole Django development stack (Django, Python, PostGreSQL, JQuery) has ecxellent documentation through and through, and I can concentrate on doing my work. Unlike certain other development environments I've used where I spent more time mucking around trying to figure out how some api call is supposed to work based on a sketchy user-provided example use-case from a previous release on a poorly maintained wiki... as the devs, who felt that writing documentation was below their station, talked amongst themselves about how cool release x+1 was going to be. That framework has all but tanked as Django flourishes.
Good documentation is one of the hallmarks of a successful project. And in my experience, if the quality of the documentation is poor early on in the project, it stays that way, no matter how much lip-service gets paid to improving it on the mailing list. Users should not waste too much time waiting and hoping that a poorly documented product will get better. Making a clean break and finding something else usually saves *much* time and frustration in the long run.