This is a bit random, but and article on engadget sparked my curiosity... Switched On: Green Plug tries to replace the worry warts (Part 2) - Engadget
The Green Plug they talk about turns off the flow of electricity to the device being charged once it has full recharged the battery. This is more efficient than charging with a wall adapter because those continue to feed power to the device even after fully recharged. This energy goes to waste.
So, here is my question: When charging via USB port, does the port lower the power being sent once the device is fully charged? I would assume some power is needed to keep the connection with the pc, but is that less than is sent out by a wall adapter?