Upload & Sell: On
you would be crazy not to spend a day in Yosemite - it is truly beautiful. And while you're at it, stop by Sequoia National Park, or at least make a point of seeing the Sequoias in Yosemite. Truly majestic trees.
Plan your lodging now, as in right this very minute. Things usually fill up 6-8 months in advance (sometimes 10-11 months for summer reservations), and you'll probably find little-to-nothing available. Some of the places around the parks are dumps beyond belief: for example, stay the hell away from the "Yosemite View Lodge" based on my (shudder) personal experience, and don't ask for details... you don't want to know.
Plan out your driving times, too... those are long distances and the travel times quoted by Google Maps or Yahoo maps will seem very long to you, as though you could drive faster, but the elevation and nature of the roads mean you travel more slowly than on an open, level highway.