While it is packed full of drooling tourons, Yosemite is truly the Mecca of rock climbing. From bouldering to aid climbing, from sport climbing to trad climbing, many of the best routes in the world are here. If you are interested in trying rock climbing there is no better place. Every great climber has made a pilgrimage here. The modern techniques and standards of difficulty were forged here. Yosemite is rivaled only by Chamonix for quality and diversity of climbing as well as historical significance. An excellent introduction to the history of climbing in Yosemite is the book "Camp 4" by Steve Roper.
It must also be said that if you are not a rock climber you really should stay away. Bears really do destroy cars constantly and the park is quite dangerous both because of the risk of falling off clifs and drowning as well as attacks by psycho killers. Every year many people die there. Stay away. Go to Yellowstone or Disneyland.