The NIC works fine both in the Mac OS and while the Ubuntu installer was running. Now that the machine is booted into Ubuntu 14.04 (64 bit) I can get no address and cannot communicate across the wire.

I know I am using the forcedeth driver.

(Sidenote, I am able to connect if I use a USB --> Ethernet dongle. The built-in NIC the system keeps trying to connect and I can use eth0 up and down all I want but it will not connect.)

Here is some possibly related information for your edification or entertainment:

Code:
$ lspci -nnk | grep -iA2 net

00:0a.0 Ethernet controller [0200]: NVIDIA Corporation MCP79 Ethernet [10de:0ab0] (rev b1)
	Subsystem: NVIDIA Corporation Apple iMac 9,1 [10de:cb79]
	Kernel driver in use: forcedeth
--
03:00.0 Network controller [0280]: Broadcom Corporation BCM4322 802.11a/b/g/n Wireless LAN Controller [14e4:432b] (rev 01)
	Subsystem: Apple Inc. AirPort Extreme [106b:008d]
	Kernel driver in use: wl

$ cat /etc/network/interfaces

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

$ cat /etc/resolv.conf 

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

$ ifconfig -a

eth0      Link encap:Ethernet  HWaddr 00:25:00:da:bc:14  
          inet6 addr: fe80::225:ff:feda:bc14/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:619 errors:0 dropped:0 overruns:0 frame:0
          TX packets:75 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:103735 (103.7 KB)  TX bytes:13853 (13.8 KB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:62 errors:0 dropped:0 overruns:0 frame:0
          TX packets:62 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:4648 (4.6 KB)  TX bytes:4648 (4.6 KB)

wlan0     Link encap:Ethernet  HWaddr 00:25:00:40:2b:d4  
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Interrupt:19 

$ uname -a

Linux [machine name] 3.13.0-24-generic #46-Ubuntu SMP Thu Apr 10 19:11:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux