Hi, my history is listed as follows:
PD: 4/98
I-485 RD,ND: 8/23/00
Assigned around mid Nov, 2001, probably on Nov, 14, 2001.
Today I checked ACM, it says "This case has been approved on Jan 16,2002".
So the time taken from "assigned" to approval is 2 months plus 2...