Finally got the port forwarding to work. Below is a video I shot on my wife's 3GS of the Plex iPhone app running on my iPhone 4. It's streaming my media library over my local wifi. Quality is unreal and the 3GS video capture does not do the actual video playback justice. After a little caching time, it plays back flawlessly with HD clarity. The next test will be to see how it streams over wifi outside of my home network.
Once I have a little more time, I'll do a new Mac Mini home theater setup with the new Plex 9.