here is official word... passed on from a Personal Injury lawyer. Waivers do NOT hold up in court! They can have the effect of making people realizing that they are doing something potentially "risky" with their bodies.
teachyoga.tribe.net/thread/aa56abb1-8926-48d4-9c52-d468d03b2c35#87d0c832-edd0-4e0f-bc1b-82f0196590d0