Air Video is an amazing app I have wished for but never thought I'd see actually happen, given the App Store's dodgy rules about approving applications like this.
The other day I had a bit of insomnia, noticed my phone on my nightstand and wondered to myself if there was any hack, any way I could somehow stream videos from my desktop computer downstairs (both downloaded video and iTunes movies/shows). I was just thinking about trying out some media server apps to see if I could make it work when I saw this pop up on Lifehacker today. I've downloaded, installed, and gotten this app to work wonderfully. You can even jump ahead to different parts of a streaming movie and it'll render in just a few seconds.
It's a pretty handy app if you use one desktop computer as a "base" for a media center with other devices (like AppleTV, iPhone, etc) talking to it. Plus, you don't have to take up any space on your iPhone (and I guess iPad eventually) with the movie itself, as it is just streamed in real time.
I haven't tested remote access outside my network, but if I could stream a new show from home to an iPhone sitting in my hotel room while traveling, I would say we're truly living in the future now.