I've got a 750gb hard drive full of music on my home computer (and a second 750gb hard drive for video). This is all hooked into my home entertainment center - I record TV on the same PC - can play all my music through my surround system using iTunes, Windows Media Player or the Media Center application in Vista.
Here's the thing - being so connected at home, I want access to all my music content when at work. I tried Orb a couple years ago with some success. This morning I happened upon Simplify Media. http://www.simplifymedia.com
I installed it on my PC, and it's searching my iTunes library right now.
It's also available as a free app on the iPhone, so I was able to install it, and within a couple minutes, I was streaming songs from my library on my iPhone!!.
I'll let you know how it works when I try to connect from work, but I'm pretty excited. I don't like having duplicate libraries from home/work/wherever, so this is pretty cool.