Recent passport renewal experience: 5 weeks for standard processing, door to door, including mail. 23 business days (2 federal holidays).
Actual time from receipt at processing center to approval: 3 weeks (14 business days).

Details (many of them!) provided below for the obsessives (like me). I got a lengthy crash course in the complexities of the passport application process and this write up ends with a few tidbits that I wouldn't have expected.

October 29 (Tuesday) DS-82 renewal (no changes) mailed First-Class USPS from metro Detroit to Philadelphia, PA

November 2 (Saturday) application arrived in Philly (4 days to deliver)

November 4 (Monday) application received/"in process," per status updated online as of November 6. Signed up to receive status update emails

November 5 (Tuesday) application fee check cleared

November 23 (Saturday) finally receive an email saying the application was received on November 4 and will take 6-8 weeks to process. New passport ultimately shows this date as the issue date, but I won't know this for a few weeks to come.

November 25 (Monday) status unchanged on website. Called National Passport Information Center to inquire about expediting since travel is beginning in ten days. They informed me the application had moved to "final stages" of processing and I should receive an email with tracking info by Wednesday at the latest, with passport arriving by Friday. A few hours after the call, a completely blank email arrives from the State Dept (this will turn out to be the second and final email I receive, despite providing my email address on the application and signing up twice for updates). Website updated several hours later this same day to reflect application "approved," but expected delivery date shown as Sunday December 1 (but Priority does not deliver on Sundays)

November 26 (Tuesday) new passport sent out via Priority Mail from Tucson, per tracking info obtained later

November 27 (Wednesday) Still no tracking number received. Called again and told the passport will arrive by Saturday November 30. I asked for and was given the tracking number and see the passport has purportedly left Tucson already. Per postmark, the old passport is sent out from Portsmouth, New Hampshire on this date as well

November 30 (Saturday) new passport finally arrives at Detroit airport this morning. Tracking still shows it will be delivered by 8pm (impossible). On this same day, my old passport (that was sent out a day later than the new one) arrives via First-Class, 65-cent mail. After midnight, the 8pm expected delivery note is removed from the tracking site, with no new date given and no change of location

December 2 (Monday) passport finally checked in at local metro Detroit post office after 1am and out for delivery at 7am. Expected delivery time 4:30-6:30, later revised to 6:30-7:30. At 7:35pm, no mail had arrived. Found carrier still delivering mail nearby and asked if he would make it to my street that night (we got skipped the previous Monday). He looks for my mail and can't find the passport along with the regular mail. I tell him it's Priority (in case it's in another section of the bins). He says "is it UPS, not USPS?" and "is it Priority Express"? (No, and I already explained I was asking because it had taken a week). He says he doesn't have it. I reiterate that the tracking shows it's out for delivery and it's critical that I get it. He finally turns around and looks through a random discard type pile and finds my passport in there. WHY. I thank him profusely and leave. The other mail arrives at 8pm. No telling when the passport would've been discovered in the random pile, but there was no way I'd have gotten it any sooner than Tuesday. 9-digit passport locator number, despite looking like a new passport number (9 digits starting with a 6) turns out to be completely different from the actual number

December 5 (Thursday) travel commences!

Takeaways: Both reps I spoke with at the call center were informative and helpful. I made, rescheduled, and ultimately cancelled an appointment at the Detroit office; it was somewhat reassuring to have a backup plan, but I'm glad I didn't need to go to all of that extra effort. Appointments were relatively easy to come by, even for the following day. The consistent theme I found when reading others' experiences is the Texas office (that serves CA, NY, TX, FL, IL and MN) tends to be much faster than the Philly office (that serves everyone else). 10 days to three weeks vs three to five-and-a-half weeks, on average (with the processing times slightly longer in the summer months). The actual passports are printed and shipped from all over the country regardless of whether the application starts in Philly or Dallas, though. The old passports generally seem to come back from New Hampshire. In light of the uncertainty interjected by the mail service (that effectively added two weeks to the overall process), expediting in person and leaving with a new passport same day seems like a great idea for next time. My experience of getting almost no updates without having to call was standard (and I actually had better luck than some people, who got no email updates at all). Problems with the passport application (usually with the picture) tend to take a full month to be disclosed to the applicant, which results in the total time being more like eight weeks. Going in person would avoid this issue as well.