Our theme is a custom one originally created for jcink (where we moved from), and was recreated for the XenForo board with permission of the original theme designer. The theme is, unfortunately, not responsive. But our head admin has been wanting a new style recently, so I definitely plan to fix that for the next one.
I've done a few custom features for the board, with the most prominent being our character reservation system (we used to track this all in a massive google doc, and it was painful XD). It tracks current and recently expired reserves, as well as clears them out automatically about a week or so after they have expired. Every time a reservation is made or extended, it also sends an alert to our Application Review team.
But yeah, for an rp forum we have a pretty large and active community. We've been around for about 5 years now, though we've only been using XenForo for the past 2.
XenForo was an amazing improvement for us. Our community was a little iffy about the move at first (the corner of the internet we most draw our roleplayers from tend to be very set in their ways and the forum hosts they'll play on -- mainly jcink/IF/proboards), but everyone adores the site we have now and all it's features.
Couldn't have done it without all the amazing support here and everyone's hard work.