There's been a good few posts on it, but I know it's a drag looking for them so....
outcome would generally be... gf3 owners experience a half-decent increase in performance (some get loads of increase, some not much); gf2 owners vary from no increase to an okay amount; gf owners experience from a slight decrease to a slight increase, but nothing extraordinary.
There certainly doesn't seem to be the 'up to 50%' increase originally touted by nvidia - but up to 20-25% seems possible on gf3s.