I'm actually looking into meteor at the moment, and the financial backing is a big plus, as it gives me some guarantee that the project will keep being maintained for the foreseeable future.
It is indeed a breeze to prototype applications with it, but I am a little bit concerned about the costs of getting an actual production ready site with it.
For intance, when is it ever OK to let your client write directly in the database, even for their own data? If you're going to pass their calls through a deny and allow call, why not just expose RPCs to the client that will handle any writing?
It seems that a lot of the light versality you have at prototyping time is lost whenever you have to get it production ready. There is definitely some value in light prototypes, but it looks like a real pain to go from prototype to production.
Likewise, I'm confused about how to get around the limitations of mongodb. Say you run a store with a finite inventory, how do you handle concurrent purchases? How about a website to enroll into classes? How about a webforum which can have exactly 5 administrators?