It must have come very far in the past few months then...based on my experimentation, it was far from being ready for production use if you needed anything beyond the most basic of SQL queries. That said, I'm rooting for it (and now, caravel). We use Pentaho, and it's....meh. A lot of moving parts, a big learning curve, and a user experience that's just ok. I'm hoping Metabase (and now Caravel) will both succeed...the open source BI space could really use an influx of simpler, beautiful tools.
A side note: I love that Caravel is written in Python. Metabase switched from Python to Clojure, and I personally believe that to be a barrier to entry for contributing. I've started down the Clojure path a number of times only to stop because I see it as something which would be difficult to impose on my team...Lisp is just so different from what most enterprisey development teams are used to. Python, on the other hand, is easier to justify. I've found things I wanted to help fix in Metabase, but having to learn idiomatic Clojure just to submit a patch is a turn-off.