It is really hard to find a "world" that has people in it, that you actually want to talk to. I have had some great experiences there though, some regular people that hang out in worlds and talk about stuff. It's kind of cool when it happens but it is hit and miss. And there is something missing with the kinds of things you can do, Super Rumble feels like a real game, but most worlds are aesthetic in nature, a place to sit and look at stuff. It feels like it needs to mature.
As I understood it, this was basically a massively expensive failed experiment so far. No-one is using it for reals (yet?).
Who's the market for developing apps for it?