I know of at least one person (smwalker) who has done a sound insulation job. I'm planning one myself with the speaker install.
For the moment, I'm planning a door, rear seat/deck, trunk, and roof insulation job using various materials. Yes, it adds weight, but I've removed enough to still be at a net loss of weight compared to stock.
The question I have is this. Is the floor worth doing? Or is the reduction in NVH so small that it wouldn't be worth it?
'09 PSM G8 GT - OPG Intake, DOD-Delete w/ Stage 1C 218/229 .600 Lift 117.5LSA, Kooks 1 7/8 Mids, Solo Axle-Back w/ X-Pipe, SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
"If you want to criticize someone else's work, be sure that your own is in order first."