Well, as I have an 08 STi, I thought I would answer the original question posted - rather than the rantings I read before me.
I had an MY03 STi before (stock) and I can tell you there is a huge difference. Especially when in 3rd doing around 60, the thing has a sort of growl that sounds prime-evil (sic) through those four tips. Cornering hard when the centre diff is locked destroys any understeer as compared with it in auto.
Talk about interest though. Every man and his dog gives it a headturn on the road.

Only concern I've had is with the DCCD. When left (acidentially) in the LOCK position, turning a full lock circle some really funny noises come from the car and it sort of stops moving like it just jumped out of gear. The booklet actually says that this is normal - but it doesn't give you confidence.

Anyway. Car is fricken brill. Beautifully finished and is a step ahead of the outgoing model. Might be a bit fatter, but is is faster. Modding will make it even faster.

I've arranged for an ECUTek tune and exhaust. Keeping with the original design, Maximum Motorsport are making the exhaust quad tipped.