We run multiple web applications, some internal-only, some internal/external. I'm putting together a proposal that we use reverse proxy servers to isolate the origin servers, provide SSL termination and (when possible) provide load balancing. For much of our setup, I'm sure it will work nicely, but we do have a few lesser-known proprietary applications that may need special treatment when we move forward with reverse-proxying.

What kinds of traps tend to cause problems when moving an origin server from being on the front lines to being behind a proxy? (For example, I can imagine problems if an application needed to know the IP address of incoming requests.)