I just picked up a brand new 335i last week. I test drove it stock, and the salesman told me about Dinan. I did some research, and found the salesman wasnt bs-ing me.
There arent not many modifications you can do for under 2k that can increase torque by 101. The torque gains alone make the car a rocket. Trust me. After the dealer cleaned the car and loaded Dinan's stage two, the saleman was dying to drive it and see the difference, and he was blown away. The car just plain pulls so much harder now. I dont have hard numbers to prove it, but there is no doubt a huge difference.
The technician who installed the software promised me that the upgrade would make me forget I couldnt afford a M3, and so far he was right.
I will call Dinan on Monday and verify the claim that I need to reprogram it...but nothing on the web site says anything about that.
I came over from the domestic pony cars, and there isnt any single mod at $1700 that can net you that much gain for them either.
If you can afford it, do it! You wont regret it.