Thanks for the suggestion, Steve. After powering-up this morning, I looked in the Kernal Log and could find nothing relating to Ethernet listed. After re-booting the machine, I looked at the new log, and saw this:
Jan 16 08:49:39 localhost kernel[0]: AppleIntel8254XEthernet: Ethernet address 00:17:f2:03:db:33
Jan 16 08:49:39 localhost kernel[0]: AppleIntel8254XEthernet: Ethernet address 00:17:f2:03:db:34
So, the only difference in the two logs is that the log from when I first booted up the machine today is missing these two lines, and there is no message or indication as to why.