Thought it was about time that I said hello - we've now been on Xenforo and live for just about a month. Overall I think our membership response has been very positive.
We came over from a very heavily modified version of vB 3.8+, and thankfully a lot of the amazing plugins that are available here have helped make the transition easier.
Thanks to @AndyB for his invaluable assistance with some questions that I had along the way and also thanks to a few other members here that I've contacted about their plugins.
We're still working on some pieces here and there, and have seen a few challenges in our implementation - mostly due to some very custom code from vB, but overall things have gone very well.
Very excited to be on Xenforo, and looking forward to seeing whats to come with 1.4 and beyond!