Sent my passport expedited. Door to door time was 20 days. I'm overall pleased with the passport office (and not USPS).

4/17: Shipped my passport Priority Express.
4/21: Passport office received application.
4/25: Check shows up as cashed. I first checked the passport tracking system at this point and I was in the system.
5/04: I receive email that passport is shipped (Priority Express)
5/07: Passport received.

The most stressful part was the USPS; during the shipment of my passport to Philadelphia they just stopped scanning after it got to the local distribution center. It still hasn't showed that shipment as delivered.

But overall I shouldn't have worried, and the stated 4-6 week wait might just be the passport service underpromising but overdelivering.