We're using Elixir + Phoenix at http://udio.ai/ (with Postgres and Mongo). It's an absolute dream to work with. Best backend environment I've ever used. There are just so many niceties one runs into at every corner: doctests, umbrella projects, :observer.start, etc.
Not just real time Phoenix with Elixir is the most exciting framework for me today. Its what RoR was 10 years back. Developer happiness complemented with crazy fast response times.
Agreed, anything performance sensitive - and a lot of apps are - is worth the shot.
At the same time, you have to be aware the ecosystem is far from being mature. I am trying right now to use MongoDB and the last Ecto adapter seems to not be compatible with the other libraries.