From my experience working with non-bike and bike chains, its something that really depends on where you're riding and your style of riding, in addition to how often.
If you always ride in nice weather, you can usually get away with lubing every few hundred miles, degreasing and full clean once a year/season. If you're a daily commuter and you ride in all sorts of terrain, then you need to keep an eye on your chain pretty much every time you get on your bike, making sure its free of debris and not kinking anywhere.
If we're talking about mountain bikes, you might have to at least wipe it down after every ride, but that depends how agressive you are, terrain, etc. Road chains should really get a couple of drops of lube every time they spin in the rain.
To cover everything, I'd say only casual riders can go by an x-mile schedule, everyone else should check up on their gear regularly and tend to it as needed.