Do heed the warnings that it's not really all that Disneyland. PA's a beautiful city, but its notoriety as a tech giant is largely shrouded by its quaint and quiet suburbanness.
My trips to the area have been very intensely business related so I don't have many tourist suggestions.
Food: Milkshake at the Creamery on Emerson and University. Beer at Antonio's Nut House on California Ave. Burger at Kirk's Steakburgers on ECR by Palo Alto High School. Slice at Pizza My Heart.
PA Places: Stanford Campus/University Ave. Take pictures, it's a beautiful campus. Apple store on University if a Steve Jobs pilgrimage is your thing. If you play any stringed musical instruments check out Griffon at Park and Margerita (I think, its near the Fry's at El Camino Real and Portage). You can't do anything other than take a picture of the HP Garage, but if you want to experience momentous Palo Alto history, there it is.
Get outside of PA: Definitely get down to Mountain View for the Computer History Museum. Apple's company store in Cupertino (1 Infinite Loop) is open to the public, go there, do that, buy a t-shirt, if you're so inclined).