As mentioned by others there is no way that an unplugged Ethernet cable can consume bandwidth. There simply is nothing to send data to in order to waste the bandwidth.
The "wall-wart" power adaptors for mobile phones are power-converters. In order to do their job they have some active components such as transformers and regulators which convert the high mains voltage down to the voltage expected by your mobile phone. Those electronics waste a percentage of power (typically around 10% of whatever power they draw is wasted by this conversion) in order to present the correct voltage to your device. Even when nothing is connected they still have to present the correct voltage at the output, unless there is a switch to turn it off, and so this is where they waste power.
Ethernet bandwidth is different, Ethernet is not a power supply device, it is used for signalling devices and over the years the electronics behind the devices have gotten more and more intelligent.
Typically any modern network router is able to "sense" whether or not a device is connected to any given port and so disable that port if needs be. This "sense" will waste an absolutely tiny amount of power but because the device knows that there is nothing on that port it will not bother to attempt to send data to it, so no bandwidth wasted there...
Even if it did try to send a data packet asking "Is anybody there?" then the amount of bandwidth it might use compared the full Ethernet bandwidth is so miniscule it would be be completely undetectable and even then I would expect this to be handled by the physical port controller rather than the rest of the hardware and so it wouldn't be able to waste bandwidth that way either.
Thanks. I had a friend ask me and I was pretty sure that it wouldn't use any due to the fact that as being said. There is no data being sent. Just decided to ask to be 100%. Didn't want to give false info. – Curiousity – 2011-12-21T20:41:23.553
6No worries, Curiousity (^_^) is a good thing and asking a question because you don't know the answer should always be encouraged. I didn't see it as false info, just a request for clarification and I was able to provide a little. I apologise if I have a somewhat harsh tone when I write, I mean no harm or offense. – Mokubai – 2011-12-21T20:52:07.143