Google Glass can be divided into (at least) two distinct parts. The camera and the display. The camera is what Google is pitching very heavily right now. I'd guess they're doing that because it's something people can relate to... taking pictures from your perspective, taking them without putting some device between you and your subject. The tiny camera that takes pictures from your eye level is a big enough draw to get early users interested. (The killer app is "real-life" DVR... why should you have to stick your camera phone in front of your face to take a picture or record a video... how many times have you thought "damn... if I just would have had my phone ready I could have grabbed an awesome shot").

The display is harder to understand. What information do you need in front of your eyes right now that actually helps you? Today you might check Yelp for a restaurant review or Google Maps for directions, but you rarely ever keep your phone in front of your face while you walk through New York... it's a reference, not a constant aide. It's a cool idea but most people (even some of the geeky ones who visit Hacker News) don't see the value.

I think the big vision here is that you'll have a camera that consumes the world around you and a system that can process what the camera is seeing, and give you real useful information about the world around you immediately. You walk into the office and the system tells you that you're looking at "Sarah" and you have a meeting with her at 3pm, or that the menu item you're looking at has 615 calories and most people who order it love it, or that the product you're about to buy is $50 cheaper at an online store and can be shipped to you in 2 days. Glass doesn't offer any of this right now... but it will some day. I want one and if I'd attended Google I/O I'd have spent the $1500 for the early prototype.