I also think Joseph is being modest
After using YaBB 1 Gold for about 6 months, I had just installed YaBB 1 Gold SP1 on our new server a week before Christmas, and saw a noticeable speed increase, just as the YaBB.Xnull team had claimed. I can only assume this was related to more efficient coding of certain areas? But then I upgraded to YaBB SE -- and I was shocked how much faster the whole thing was. Its even faster than vB (by quite a bit, from what I've seen).. and to be honest I can't say I know why, but there it is in black and white... my board is significantly faster than several vB's I visit.