Yer look I am in the process of building something along the lines of what your talking about myself. I am a software engineer, been working with Microsoft tools for years and just recently crossed over to the apple platform. While it is early days yet, I am quite confident I can make it work, my plan is to build a door opener with the iPhone. My plan is to use the Arduino connected to a PC on my WiFi to talk to the iPhone and give it the commands to open the door. Communication to the Arduino is pretty straight forward, I'm going to use Apple's Bonjour protocol to talk with the iPhone and the Server. My Server is just a Win XP box which has a few other functions around the house, but I think I will build a client that can run on the Apple Mac machine too.
I was also thinking for future expansion I could build in PIR detection, so you would be notified when someone approached the door, and a Camera interface so you could see the person at the door on the iPhone and then hit a button to allow entry.
If your interested in something like this too, drop me a message firstname.lastname@example.org
and I will let you know how it goes!