I work for a company that uses it as a mission critical product. It provides the search in our SAAS. I'd say it mysteriously fails 3-4 times a year. But no one wants to invest or encourage anyone to look at it proactively or even re-actively. We've had JVM issues and indexers spiral out of control using 99%CPU only to stop at random hours later. It's definitely a product to learn before it fails.