Super fast and super slow receipts

I've experienced both super fast and super slow receipting from USCIS:

- Efiled an I-539 on Tuesday and got the receipt in mailbox on Saturday. It only took 4 days including mail delivering time. I can't believe the efficiency of VSC.

- As a July 2 filer, I just noted the receipt was sent on 9/13 and not in my mailbox yet. It took about 90 days. I can't believe the efficiency of NSC.

USCIS, love it or hate it? You tell me...