Here is my experience getting a passport renewed last minute at the San Francisco Passport Agency.

I realized 3 days before departing the country that during my trip, my passport would expire.

• I called the Passport Agency and after navigating through the phone tree to talk to someone, I was transferred to another person who said to come in before noon and they would be able to help me.
• I went to the SF Passport Agency building
• Told the guard that my flight was in 2 days and he let me in
• Went to window #3 and spoke with a rep
• I confirmed with her that I had
  • my form filled out
  • my existing passport
  • two passport photos
  • $135 in check/money order/credit card (not cash)
  • proof of my flight (plane tickets)
• She looked at my plane tickets and gave me a number, saying to wait till it was called
• I received ticket #68 at 9:42am on a Monday
• I was called up at 10:41am (about an hours wait)
• I gave the rep my existing passport, my photos, and my form
• I showed the rep my plane tickets
• I paid $135 with my credit card
• I got a cliam ticket
• They said to come back the following day between 11am and 4pm to pick up the new and old passports