Waivers are no good. You can not sign away your rights. And besides, a waiver would seem to indicate you KNEW there was a problem.
Waivers are in fact valid when used properly, and "you knew there was a problem" is EXACTLY when they are valid. But the "you" is not the host, it's the attendee.
Accountability for negligence can not be avoided by a waiver of liability - if equipment is not maintained improperly, or an attendee is given bad information, compensation for resulting injuries is not waived.
However, an attendee "assumes risk" by participating in some activities, even if he does not sign a waiver of liability. A skydiver who sprains an ankle, or a sports fan whose nose is broken by a foul ball, isn't likely to win a lawsuit. Signing a waiver of liability acknowledges this assumption of risk.
So a waiver that says "even if I'm in the wrong, I'm not liable" is, as they say, not worth the paper it's written on. But a waiver that says "I'm liable under thes circumstances, and not under these, and you agree to participate knowing that" usually holds up if challenged.
JAC