Obscuring the windows during decorating

SailorSam

Windolene or watered down Emulsion, although the paint is harder to get off once you're finished.

PasturesNew

If you don't want it to look like a squat from outside, then you can get some expanding net rods that you just twist out to the width - and you can get some net curtains 2nd hand at the charity shops.... turn the curtains upside down and slide the pole through the hem. Cut to size.

If you're a bit posher, there are actually some disposable paper blinds you can use for this purpose. They are very lightweight and stick on with double sided tape/similar. Try http://www.blindsinabox.co.uk or http://www.redishade.com http://www.thecaliforniacompany.co.uk http://www.premiershutters.co.uk/temporary_blinds.php - or google for things like: paper blinds, temporary blinds, instant blinds.... should be about £5 each.

lagi

Depending on how high your window is from the road/pavement, why not only put paper/carboard/windolene 3/4 up the window, high enough to stop the average nosy person but still allow light out and in.

Have seen a few houses with newspaper but none of the others, newspaper again during the day wouldn't be too dark.