I just installed a ($35 shipped, Ebay Brand) Engine damper and all I can say is WOW..
G35 engine torque damper - inexpensive
G35 engine torque damper - brand name part
The throttle feels "Crisp" and the car is much more rigid. The soggy stock throttle feel is gone. It's an amazing upgrade!
There is slightly more vibration in the car but nothing too bad. Also you can feel the engine in the pedal more.
The only thing that worries me is the mounting point on the timing cover... Since it's aluminum I fear that it might strip the threads on the bolt or crack over time.
Anyway... if you don't have one go get one now!!
Install took about an hour and was rather simple if you have the proper tools.
I say the proper upgrade list for the G35 would be this..
Engine Damper > Intake Spacer > Z-Tube > Exhaust > Suspension > Wider Wheels (9.5" or wider) > FI
Modified by Kenrik at 8:35 PM 4/26/2008