Should I disconnect my MacBook Pro's power cord when the battery is fully charged?
You do not need to disconnect your MacBook Pro's battery. Your battery will stop charging once it is full. Apple's modern batteries are much smarter than previous designs.

To get the most out of your MacBook Pro's battery, follow the Notebook Battery advice from Apple: unplug and use your battery until empty about once a month, then charge back up to full.

At the time of answering, Apple's advice read:


  For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time. An ideal use would be a commuter who uses her notebook on the train, then plugs it in at the office to charge. This keeps the battery juices flowing.


If you need help following Apple's advice, use Battery Guardian; it is free and will remind you when to deplete your battery.