Mark, a window made from liquid crystal glass looks like a standard glass window but is actually like a giant "LCD Screen" with two states: opaque and transparent. My understanding is that when current is provided, the window is transparent. When no current is provided, the glass is opaque. Here is a link with example photos:
This obtained from a newsgroup thread: Saint-Gobain quotes a lowest price of 1700 euros per square meter installed. Big coin! About $3,600 for a 3'x6' window
LCD glass doesn't really block that much light, so it wouldn't be useful in a home theater setting. It's good for privacy glass though.