Japanese company Micro Reactor System Co. is going to market this year flexible and thin (0.025mm to 0.4mm) electronic curtains.

Liquid crystal molecules are dispersed between two panels of plastic. The curtain is opaque when turned off and becomes translucent when the power is turned on.
This curtain can actually be made to appear white, red, yellow or blue.

I am actually looking for something like this and have not found a solution that is affordable and reasonable to install. I want to be able to dim a large glass wall in my living room. When lowering my projection screen, I could just push a button and dim the glass wall. This would rock!
The electronic curtain will sell for 30,000 yen ($267) to 50,000 yen (~$445) per m2 later this year. This is still rather pricey for large areas. I hope the prices come down a bit.
More details on Nikkei.Net (Subscription).

See also the electronic Glass by Innovative Glass Corp.