The biggest "Wow" moment of Tech-Ed for me was when I saw a demo of Indigo. Before Tech-Ed, Indigo was just an overhyped buzzword to me. However, at the convention the Indigo demo was one of the most impressive things I saw. The demo was done by Microsoft employee Ami Vora. In the demo, Ami came out with medical sensors attached to her head (brain wave sensor) and her hand (blood-oxygen level). This info then populated into a Web-based console that could be used by a medical professional. This console showed a live, moving graphical read-out of Ami's data (just like those machines you see on the TV show "ER").
The impressive part came when Ami said that this info was on a LAN, and that a doctor may want to access it from home during the evening. But rather than having a doctor connect via VPN or call someone on the staff and give the readout over the phone, the IT staff might want to allow the doc to access it over the Internet. So Ami went into the XML file of this Indigo-powered app and simply changed three variables - 1.) send the output over HTTP, 2.) encrypt it, and 3.) require the doc to use a smart card to authenticate. In the past, it would have taken a lot of lines of code to redevelop the app to include these features. In this case, an IT pro could simply make the changes in a configuration file -- and didn't even have to recomplile the code for the app. After Ami made the changes, she switched to an Internet connection, connected, authenticated with a smart card and then saw the exact same Web-based app with live data running. When the IT pros in the Indigo demo saw that, most of the mouths in this session were hanging open.
Indigo is part of the new .NET Framework in Longhorn. This link provides some more details.