Network Interface shows up... eventually
Just wanted to confirm what someone else said: I'm using FreeNAS-8.0.1-RC1-amd64 (7508). I switched network cards to use the internal NIC, and when I restarted the system I had to use the console interface to define the internal interface. Once I did that though, the card STILL didn't show up on the Web GUI. However, after waiting for a half hour or so, I went back to the reporting tab, and it was suddenly there!
Not sure what the delay is caused by, but I'm guessing that the Web interface has to gather some amount of data before it will generate the graph.
In any event, it's working great now.