Debris disks are dusty, gas-poor disks around young stars, generated by collisions between parent bodies and/or sublimation of comets. The Spitzer Space Telescope has enabled photometric searchs and detailed spectroscopic studies of thermal emission from dust in hundreds of debris disks at mid- to far-infrared wavelengths. These observations allow us (1) to infer the spatial structure of dust in individual systems and determine how the dust grains are removed; (2) to measure the disk fraction (in young associations and moving groups) as a function of age to constrain the mechanism that triggers collisions, and (3) to place constraints on the mass of circumstellar molecular hydrogen and therefore models for giant planet formation. In this talk, I will discuss the spatial structure and removal mechanisms of dust in debris disks, and constraints on the models for the formation of gas giants and the late-stages of solar system evolution. I will also describe outstanding questions about solar system evolution that can not be addressed with Spitzer and will require future ground- and space-based instruments.