Ernesto Colnago came up with it as a marketing tactic back in the 1980's, if I recall right.

The truth is that it's cheaper and faster to buy unbent blades and stick them in a crown without bending them. All Colnago had to do was design a crown with the necessary forward angle to the blade sockets to achieve this.

Does it do anything? Negligible. It's all about style - and I've yet to see anything look good with straight blade forks. Your mileage may vary.

-Kurt