According to travel.state.gov – the official US Department of State website

Routine service: As of ( Monday May 3, 2010 ), we are processing routine applications in approximately 4-6 weeks from the time of application.

Expedited service: As of ( Monday May 3, 2010 ), we are processing requests for expedited service, that include overnight delivery to and from the Passport Agency, about 2-3 weeks door-to-door*.

You can use FastPort Passport to obtain your passport as quickly as 24 hours. Click Here for passport services.