Keep the shades up

The lights dim for take-off. Traditionally, we turn the lights off and open the blinds for take-off and landing so as to orientate the passengers inside the plane. In the event of a crash, it helps if your eyes are adjusted to the light outside, and the emergency path-lighting is more visible as you sprint up the aisle. There is, however, another much more sinister theory... : the plane blinds are raised so that in a crash situation - statistically much more likely to happen during take-off or landing - it is easier for the emergency services to count corpses through the windows, instead of having to board the plane.

Air Babylon, Imogen Edwards-Jones & Anonymous

Further poking around revealed this from WikiAnswers:

The reason why they want all shades up is because, airlines rely on passenger's vision of the whole outer aircraft. The only people who can see the engines and what happens in the surroundings, are their passengers. Crew who are seated at their crew seats, will not be able to see a whole lot of the plane's exterior. And obviously, planes do not have rear view or side view mirrors.

Thinking from a passenger's point of view, if you see something wrong going on outside, you would panic and call for the flight attendant immediately. Right? So that is how, flight crew would be alerted if anything goes wrong: by the passengers.

As for closing them at night, it differs with airlines. Most major airlines (SIA, MAS, Cathay pacific, Qantas) would still ask you to have it remain open, but they will turn off the cabin lights. (I actually don't know which airlines would ask you to close the shade as it is a safety procedure) Same thing, when you turn off the lights, you would be able to see the outside of the plane and report for anything that goes wrong.

Also, in any case of emergency, you will know not to go to the side with fire, or submerged into water by looking out the nearest window.

While we're on it, I also want to know why seats must be upright. The answer is so simple and common sensical I don't know why it didn't hit me.

Essentially it allows the easiest escape access for passengers in case of emergency, as opposed to having to wriggle over seats in various levels of recline in an already very tight space. When upright, the seats are locked and less likely to get unbolted. Also, if you're lying back, chances of your head getting tossed around and breaking your neck is higher. Plus, an upright seat makes it easiest for passengers to employ the brace position - something about being over knees, hands over ears or head.

Anyway, Air Babylon is not as interesting as Fashion Babylon but still, not too bad as a frivolous read.