A few weekends ago I was testing my new SageTV setup with my laptop.
I had the network in one configuration, and I wanted to move things around to get better reception. Before I moved the server and aerial, I took the Powerline device to different rooms in the house to test. I ended up only getting 9.4Mbps in other rooms. I then noticed my laptops Ethernet connection was at 10Mb, assuming something was wrong I forced it to 100Mb full duplex and only got 17Mbps throughput. Assuming this was due to some cross circuit performance problem I tested around the house, and ended back in the office, and with my laptop on the same 100Mb switch as the server, I was still only getting 17Mbps.
After banging my head for a while I put the network connect back to auto detect, and plugged the laptop back into the power cord and ta-da, 94Mbps to the server.
Thus for my Dell Latitude E6400, with Windows 7, on battery, the Ethernet runs at only 10Mb. I remember Windows XP having an option for reduced Ethernet speed on battery, but cannot find it under Windows 7, it just seems to always be on.
Thus now with power cord in hand, I found that the room I wanted to place the server gets 45Mbps to the TV, so I proceeded to move everything, and over-the-air TV is wonderful.