New material from dupont might cut auto weight significantly
 

There's nothing like a bit of resin...found via ABG:

I suppose the next question is how much will this stuff cost once it's popular? Metal is pretty cheap for these applications.

And also, how much will it cost to work with.

hmmm, i have some projects i wouldlove to use that on ......

a quick google search makes it look like it's other commen use is knive and gun handles?
it seems to me that if you can replace your exaust with a high temp plastic that could be cast in to the shape insted of stamping out shapes from flat metal sheats, forming them with a die and press, crimping them together, welding them, giving them a coat of rust protection, and repeating every 5 years as they rust and fall appart... plastic exaust sounds a bit hokey, but some plastics hold up to heat rather well, and this sounds like it could be on the top of that list.