i joined the Terraria unofficial forums which run it. Thought it was rather shiny and seemed the business. Still playing with it, but haven't tried it from the site owner side. Very interested in it because of the talk of bridging it and wordpress.
I looked into it a couple of months back. From what I recall the developers used to work on Vbulletin at one point ...
It looks very nice, but I'm yet to come across a site that I'd frequent that uses it
If anyone has any examples of sites using it I'd love to have a poke around