How long is it safe to go away and just “leave” a cat?

Our question this week was:

Dear Dr. Jon – we are getting ready to go away for vacation. We will be gone for 4 days. I generally just leave a bowl of food and water out and the cats do fine. Is that okay in your opinion? 

For Dr. Jon's answer:
Hover over this web link for Pet Place article...........

http://www.petplace.com/cats/how-long-is-it-safe-to-go-away-and-just-leave-a-cat/page1.aspx#!