I gotta say I absolutely love 650b….on the road. I can run a nice fat, super supple Grand Bois Hetre that makes rough pavement disappear and allows me to easily do rides that are a mix of pavement and dirt roads/fire trails. That said, I really don't see the point of 650b for dedicated trail riding. If you want to ride a rigid bike or race XC then 700c/29″ makes more sense. If you want to ride technical trails then 650b offers nothing over 26″. 650b on dirt just doesn't seem to be difference enough to make a difference. Also the name - 27.5″ - is stupid. Then again so is 29″. There's no need to make up a new name for a size just because it's intended for the dirt.