What is a waiver of liability and how effective are they with regard to personal injury claims?

Waiver of liability releases have become quite popular nowadays especially with respect to activities which invoke an inherent and dangerous risk, such as sporting events amusement parks. Ski slopes, skating rinks, bungee jumping booths, etc have become infamous for having participants sign these waivers. Courts have been known to find that these types of activities involve a known risk and therefore the participants in the sport are said to have voluntarily waived their right to recover, even without the liability waver. This assumption of risk can even apply to those attending events such as baseball games or hockey games and being injured by a stray ball or stray puck. This type of personal injury claim has usually come down on the side of the park owner or event sponsor.