I've just had my first experience with AppleCare. My 1 year old MacBook lost all track of its battery - the little battery icon in the status bar showing X, when I plugged the power cable in the led just showed green at all times, and when I turned the laptop upside down and pressed the monitor button on the battery I got no little green lights - others have had the same problem.

I called up AppleCare and tried a few things, installed an upgrade, turned off and on again whilst holding down a combination of keys, etc. They suggested I take it to one of the service providers in my area to let them determine if it was a battery or a connection problem. Instead I trotted off down to Solutions Inc and the guys in there kindly let me try one of their batteries and pleasingly it all worked without a problem. So, on Monday morning I called AppleCare back and told them what I'd tried. End result, a shiny new battery which arrived today and I now have a laptop which is no longer tethered to the mains :-)