My I-751 time line
Hi, All! This is my time line, I reside in Maryland:
1) Documents received at Vermont SC on December 13th 2010
2) NOA with 1 year extantion received on December 27th 2010
3) Notice to appear for biometrics received on January 14th 2011
4) Biometrics taken on February 8th 2011
5) On line status changed from "initial review" to "card production ordered" on May 12th, 2011

6) Post decision activity (on line) - an approval notice is mailed on May 13th, 2011
I haven't received neither my GC or the approval letter in the mail yet but I hope it will arrive soon, it does say on the website to allow 30 days for it to arrive.
I hope this helps. My both green cards processes were quick and painless and I wish you all the same.
To the guy who filed in November and is still waiting for biometrics appointment notice: You should call them ASAP, this is unusually long timing, they sometimes loose documents, call and ask, it won't hurt