Although I did not firsthand upgrade our current version of UBBThreads (6.5.1), I did sign the approval... mainly based on the support I have received here, not at UBB. This community is by far, the best I have seen for a software product like this.
However, we also considered FusionBB because of our faith in Josh and what he has contributed here (we would have done it now, but was uncertain if Fusion was developed to the level we were accustomed with Threads). I think this time next year, if we anticipate a smooth transition from Threads to Fusion, we will more than likely go that route because it is my belief that Josh and the other developers do really care. And in the community I moderate and administer, trust and dependability is a vital element (this is not to say the people of Infopop/UBBThreads are not supportive... they have been wonderful! Hence, one of our intitial reasons for implementing this product).
I look forward to a long and productive relationship with this and the next like community (i.e. either any unforeseen Threads releases or Fusion).
Ciao!