My dad reckons you should leave them open because having them closed for a week implies the house is unoccuppied - he also leaves a light on towards the back of his house.
In my house we have the curtains closed most of the time anyway even when we are home

so it won't look suspicious if they are closed when we are away
-Office has a black out blind permanently up
-Spare room has the blinds down, we rarely go in there
-Master bedroom usually has them closed because we don't want people looking in at us and we are too lazy to close the door to the ensuite
-Lounge I prefer having them closed because we are somewhat overlooked
-Dining room we don't use much and can't be bothered to go and open them
-Kitchen doesn't have any
Exceptions tend to be if we have visitors or have recently had a good clean and tidy up, not so embarrassing to have people looking in then!