I used the Arduino and a camera to make a weather proof box to take time lapse movies. You can see my write-up/pictures/movie here: http://www.glacialwanderer.com/hobbyrobotics/?p=124
The basic premise is to run an Arduino as a timer and once an hour it turns on a relay. The reason for the relay is minimize power usage while the Arduino is running as a timer. When the relay is powered up the servo and camera also get turned on. Then the Arduino uses a servo to turn on the camera and take a picture.
Some of the most interesting data I collected during this project was the current use from the 12 volt battery. The current draw when the relay is off is only around 0.07 mA. I had no idea the Arduino used so little power (0.84 mW)! The current draw when the relay and servo are on is around 210 mA. The current draw with the relay, servo, and camera is around 300 mA. But remember these higher current draws only happens for a few seconds while you are taking a picture.
If anyone has more questions about this just let me know.