We have an automatic Cat Feeder which seems to work really well. Despite it having 4 compartments, which on it's max setting can open 1 compartment a day, I'd be loath to leave the sweeties for that long.

It really does depend on the Cat. Sooty seems to get lonely enough if we leave her for 1 day, while one get's the feeling that Whiskey would be fine on his own for a week if the food lasted that long.