I have a 1GB LAN with several 1GB switches connected to devices capable of 1GB file transfers. Now that I have replaced my 1GB Netgear router with the U-verse 3801, will I still get 1GB speeds for LAN file transfers?
No, the 3801HGV has an internal Fast Ethernet switch only (10/100 Mbps).
What you need to do is maintain 1Gb switches throughout your network, and uplink one of them to the 3801HGV. That way, the only traffic going through the 3801HGV is traffic to/from the Internet. All of your LAN traffic will only go through your own (1Gb) switches.