It's a mixed belief because there's different theories on what's best for the car. Every car manual says some type of break in period yet there are people that go drive like a bat out of hell the second they step into their new cars and never have any problems with them. I like to be on the safe side though and take it easy.
Question though since I do only have 170 miles on mine so far. For those of you that have your STi's, did you keep it in "I" mode the entire break in period and switch it into "S" mode at all? I've had mine in "I" so far keeping it under 4K rpms but it feels so sluggish in "I".