Linus Tech Tips forum and there's quite a number of game publisher/developers that use it such as WildCard (Ark Survival), Obsidian (Avowed, Pillars of Eternity, Grounded). But most of them I know actively hate it and it is the pain of having to migrate a large forum with custom development that prevents them from migrating.
IPB has kind of catered a community similar to Apple, where you are happy with what they offer you and you try to stick to what they decide (at least since v2 and after). I do not see many large add-ons such as the ones you or [USER=5364]@Bob[/USER] make, and when I was looking at them to see if they fit the needs for a community most of the add-ons I was looking at were actively abandoned or buggy. I also find the styles to be very samey and lacking much originality now in comparison to back in v1/v2, where people like [USER=1173]@Kim[/USER] would often make designs that drastically changed how the forum would look (much to my frustration when having to code some of those headers 
).
The biggest flaw with IPB is the attitude. They do not easily take criticism, they do not like to hear opinions counter to their own, and they often make decisions that upset people and then punish those people for speaking out. Every general **** up by them (such as perpetual licensees) has been met with substandard customer service, and they then just continue to do the same thing over and over.
People can say what they want about XF (literally), but building a business or community you intend to invest countless hours into is much better on a platform that will actually treat you like a customer, and at least let you speak your mind (within reason).
