The good news about hhvm is that with the newest builds from the past few months you can finally run it longer than a week without memory leaks and crashing under high loads.
If you look at the changelog, you can see it really is a beta product that people use in production anyway
This is what caused me to abandon HHVM for plain ol' PHP around a year ago. I was running it in Docker containers and the memory leaks would regularly crash my containers if left unattended for more than a couple of days.
It was quite frustrating because I noticed some definite performance gains (e.g., ~2x faster page loads, etc.), but ultimately opted for PHP's stability.
The benefit to running all this in Docker is that I can swap HHVM back in relatively easily (unless it's changed really dramatically over the past 10 months or so). Your comment has me tempted to give it another shot!
If you look at the changelog, you can see it really is a beta product that people use in production anyway
https://raw.githubusercontent.com/facebook/hhvm/master/NEWS
"Ditko" 26-Feb-2015 finally solved me having to restart it every several days
I'm very eager to compare PHP7 in production