Don't laugh! One company actually proposed such a thing! Their theory was for a hypersonic trans-pacific service, like to Tokyo, Sydney, etc. in a fraction of the current time by sending the craft up to the edge of the atmosphere and basically bouncing it up and down off the edge of the atmosphere in a form of pulse and glide in and out of the regions of usable air. Undoubtedly they eventually realized that might be fine for cargo and hardy pilots, but not good for passengers.
EDIT: Well that didn't take long to find..
Info link
