We were upgraded to concierge once at the BC... never figured out why because we booked a standard view non-concierge room. It was a great surprise!
Besunnysideup, concierge usually has a lounge with food and beverages for breakfast, lunch, afternoon snacks, dinner, after dinner dessert (depending on the resort). It's not intended as a meal replacement -- usually it's finger foods. There are dedicated staff that can help with ADRs, shows, tickets, etc. Turn down service is included each evening. It's an extra level of Disney magic and pampering.
Sometimes, like in Disgal1's case, the resort (concierge is available only at deluxe resorts) will code the room key to allow access to the concierge floor at the resort. Usually you have to slide your room key into a reader on the elevator and then press the button for the concierge floor (otherwise, it won't work).