We use it semi-regularly at work. (I do Linux Administration for a hosting company.) Or, more precisely, our Oracle team uses it, as there seem to be several Oracle-related utilities that require a GUI. I don't work with it directly, but I have helped to set it up on that team's behalf from time to time. For that purpose, it seems to be quite stable.

I don't think X-forwarding is a good substitute for VNC(-alikes) if you need to do long sessions, but for occasional one-off GUI work where either there's no CLI equivalent, or the CLI version isn't the best choice, it does get the job done.