I've been using XParticles for a while now, mind you, not in a production environment at all. I've been using it in my freetime to do some abstract artwork and get used to the plugin before I am willing to offer it as a skill to clients.
I think it's a great Plugin, it hasn't crashed on me once and every single time something didn't work and I rebuilt it I noticed that I screwed up some setting. So no, I can't confirm that rebuilding stuff from scratch magically fixes some scenes, but I don't deny it either. I haven't used their tech support either, except once when I bought my license (used) and it didn't show up in my account. I got an answer in less than 4h every time. I think some of XParticles systems are very obscure and badly documented though especially since a lot of functions have been depracated and moved to other parts of the plugin. It's sometimes hard to get a clear answer to very simple questions. Their videotutorials are great though, learned a lot just by watching them.
I haven't used the forum for the sole reason that it seems to be dead so I never bothered even registering so I can't comment on that.
All in all though considering that's a plugin and not a dedicated software and the amount of features it delivers it's fine for me. As I said, I haven't really encountered any severe bugs or issues.