Excellent product, we have some clients who are very pleased with XenForo.
We are trialing a large forum with over 4.9 million posts and saving changes in the admin is taking some time. I understand your checking permissions when you click the button but I think it's worth changing the buttons so you can't click them twice. We've had a couple of instances where we've tried to added a new forum and it's been created twice as we thought the previous request had hung.
Hope this helps.