My startup uses it in production. We probably send a couple million events a day and have a big dashboard with around 40 graphs on it. We also have other dashboards split out for viewing specific things. It works pretty well once we got MongoDB tuned properly. We're receiving events via UDP (which we had to add in, but is supported out of the box in the new version, I believe)

I don't think it's meant to be used as a full-on data warehouse. The closest thing people usually compare it to is Graphite.