Varnish looks like a great reverse proxy - and the next network / server I setup, I'm planning to use it. I'd like to do something like this:
PFSENSE -- VARNISH -- APACHE2 / NGINX
That way, I can firewall and failover with pfSense, cache with Varnish (maybe even failover and/or load balance too?), serve dynamic content with Apache2, and static content with Nginx.
HA! I just realized that since I'm already using pfSense as my firewall it was a trivial task to point the load balancer to port 6081 instead of port 80, and point varnish to port 80 instead of 8080. I'm now running varnish in production! :-)