When coming out with a new version of a product regardless of the importance of a new (or existing) feature ... EVERY forum feature must be weighed against it's payload - an inevitable reduction in overall speed. I find other forum software slow (vB, IPB) and I find the forum experience is wrecked when I have to wait and wait.
Speed über alles.
Stay skinny my friends.
According to you, Xenforo's best attribute is ....