My recent data point:

11/27 – mailed to Philadelphia Priority mail with tracking
11/29 – delivered at 5AM
12/1 – Check for fees cashed
12/6 - Early AM– Email received – processing application, locator number issued
12/6 - Late PM – Email received – Processing finished, overnight delivery notated, should receive on or about 12/9
12/7 – Received new passport by Noon

Very impressed. With regular / routine processing and paying for Next-Day return, I received my new passport in 10 days!

When I initially tracked its progress and saw the boilerplate (4-6 weeks), I was actually worried a bit about travel for New Years.
Very happy today.