This is one area of the US government that (nearly) unfailingly works well. As a nationalized citizen by marriage, I often expect more problems, but have been pleasantly surprised.
My renewal:
Tuesday, week 1: mailed in form, used expedited servie
Fraiday, week 1: notified that it was received and being processed
Monday, week 2: notified that passport approved and was sent to printing (also the ID / Password)
Thursday, week 2: received passport
Tuesday, week 3: received ID / Passcard
Wednesday, week 3: received old, cancelled passport
When I compare this to my other nationality (Belgium) it is much simpler, as can be done through the post, and leagues ahead of where our official residency is (Italy), where "normal" citizens wait 8+ months for passport renewals..