I live in San Diego, CA. A big military city.

(I think we're the biggest on the west coast)
I think that if designed right, you could draw some nice traffic. Military personnel often go out for 3-9 months, and have difficulty comminicating with family. I doubt that people would use forums to send personal messages to family, but it may be a nice place for the general public to send messages to military overseas.
You could also have a Rant&Rave for people to discuss politics and whatnot.