I\'m wondering how mature and stable D is, and if it might be a good replacement for C/C++.
I know that there are currently two standard libraries (Phobos and Tango). Is
I don't think the question of replacing C is about whether a potential replacement is "good" or "mature" enough on a theoretical level, but rather about practical considerations and the fact that C is "good enough" for what it's used for. Unless a language has complete native build and runtime environments for every major operating system out there, it's not really practical for what C is used for. The fact that C is the language of POSIX is a big part of the whole issue.
Surely other semi-low-level languages like D could have great applications in specialized fields. But you're unlikely to see major multiplatform software (web servers, database servers, word processors, web browsers, etc.) written in D because no major OS (much less all of them) comes with a D build or runtime environment.