Definitely go into the city, even if you have just 5-7 hours. You should try to see Cerro Santa Lucía and the Plaza de Armas.

If you're feeling adventurous, wander north across the Río Mapocho to the Parque Metropolitano. Ride the "funicular" (old-fashioned cable car) up the Cerro San Cristóbal to the "Cumbre" station, where you can see the majestic "Virgen" statue overlooking the entire city (and its blanket of smog). From there, you can ride a longer cable car to the east for some amazing views of the city! Very reasonably priced.

I highly, highly recommend the restaurants in Barrio Bellavista (right outside the entrance to the Parque Metropolitano).



If you don't have time to go into the city, but you do want to leave immigration, at minimum you should go to the Gatsby café/buffet/restuarant/coffee shop. It's on its own special mezzanine level above the ticket counters, has great views of the tarmac and terminal, and is open 24 hours a day.