Question of the Day: Shoe Swap!

I’ve been thinking lately that it’s about time to replace some of my shoes. And considering how bad I am about parting with shoes, I’ll probably continue thinking about it for a while before I actually do it.
How often do you replace your walking shoes? Do you keep track of your mileage and replace them after the recommended 500-600 miles? Or do you just go by feel or some other factor?
I tend to go by feel/condition. But I definitely start moving over to different shoes when I hit that 500-600 mark.