OK, well back to the original topic, I was thinking about this a bit, and it is pure speculation.
What kind of case does IB have over a "look and feel" copyright, if that's what they're going for? I can't see any other type of copyright that they could claim, as weak as it is anyway, with the hundreds of other forum packages out there that came along before vBulletin.
Is vBulletin thinking they own the plug-in/hook system, as that to me seems the only thing that could be considered "revolutionary"? But most if not all MVC systems that xenforo is built on use the idential nomenclature and features.
I just can't see what it is that IB has "copyrighted" that xenforo is using. It would seem to me that there'd be a lot of prior art out there that could be used against IB, meaning it'd be harder for IB to prove a copyright violation than it would be for xenforo to claim prior use/art, in my opinion anyway.
Mike and Kier have taken the high road to not allow IB bashing here, but IB doesn't seem to mind customers bashing their own product on their own forum, and keeping multitudes of posts revolving around the Xenforo competition, and who's moving to it. It seems strange to me.