I have heard some people are running disc springs as clutch springs. They should give a more contant (less temperature sensitive) clutch and by using more discs on each other it is possible to controll the strength.
http://www.schnorr.de/en/germany/pro.../disc-springs/

Anyone with experience ?

I also found the same kind of springs to give a pre-tension on bearings, sounds like an idea to use is as shim to fill up the end play.
http://www.schnorr.de/en/germany/pro...disc-spring-k/

More info:
http://www.schnorr.de/uploads/media/handbuch_en.pdf