I just checked my mail and I got 2 letters too. One was the i-797c notice and the other is notification that full payment was received. It goes on to say they will notify me by mail about my biometrics.
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State: New Jersey Applicant
Sent: Priority mail sent 9-29
Delivered: 10-1 at Chicago Lockbox
G-1145: 10-4-12 routed to California
I-797c: 10-9-12
Biometrics appointment: 10-29-12
Walk In: 10-17-12
I-821 approval: 11-2-12
Ead Arrival: 11-13-12
Ss card:11-15-12
Dl: 11-28-12