I'd like that to be true, but I think it's still some years away from being a similar experience. Sage is impressive but still very much shows its seams: it's trying to glue together a bunch of separately developed projects, with their own ideas about things (everything from Maxima to R), and the glue is often pretty noticeable if you do anything remotely complex.
(That said, I also avoid using Mathematica for most things because I'm squeamish about ending up with any significant project too closely tied to a proprietary platform.)
(That said, I also avoid using Mathematica for most things because I'm squeamish about ending up with any significant project too closely tied to a proprietary platform.)