The break in period lasted all of 2 days for me... had my STi for a week today and have 1400 km's on it...
Last night was the first time I had some fun with it, and caught a couple hondas underestimating it. Nothing ridiculous, but got them by about 2 car lengths in an intersection then slowed down.
I'm sure it'll be more fun when they see you in a suit. hahaha
But yeah, it's sweet.