Let's look at the specifications first. Google states that Glass has a 'high resolution display' that is the equivalent of a 25" HD screen eight feet away from the eyes. It has 12GB of usable memory (16GB total), and, of course, it syncs with Google's cloud storage. Camera-wise, it's got 5MP for photos, and 720p for video. Naturally, Glass has the usual communication options such as Bluetooth and wifi. The battery supposedly lasts for about a day of typical usage. For an entirely new class of device, it's hard to gauge what these specifications really mean.
Google has also released the companion application for Glass on the Play Store, dubbed MyGlass. It requires Android 4.0.3 and up, meaning about 54% of Android users are covered. Since Glass will most likely be something for enthusiasts - even when it becomes available to the general public - this seems like a good enough cutoff point.
Google also took the covers off the documentation for the Mirror API programmers will use to write stuff for Glass. It's got everything from quick start guides to code samples, and everything in between that you need to get coding. The Mirror API has been detailed before, for instance in this talk by Timothy Jordan.
Lastly, the terms of service for the Mirror API contain some interesting surprises. For instance, programmers are not allowed to serve or include advertisements in their Google Glass service, nor are they allowed to charge for them. In addition, you are not allowed to use user data obtained through Glass for advertising purposes either - you can't use it yourself or forward it to an advertising agency. I'm guessing this is done to make sure Google attracts the right kind of developers - enthusiasts who are in it not for the money, but for the excitement of a new class of device.
On top of all this, you may not distribute your Google Glass programs outside of the "official Google-hosted Google Mirror API Client distribution channel" (rolls off the tongue, doesn't it?), which is a strict departure form Android. We'll have to see how this holds up in the future.
I'm quite jealous of the lucky few who'll be getting Glass soon. It may not go anywhere, but that doesn't make it any less futuristic.