This is fairly old technology. It works pretty much like regular Ethernet, when you stop to think about it. A hub or a Layer 2 switch (which is every home switch) broadcasts all traffic in the same network down all lines, and the same is true on responses.
I think that as long as the speed is faster than your ISP, you will be fine. If you have a 3 Meg down speed and the thing is an abysmal 10 Mbps, that's still more than three times faster than your ISP. I don't think it will have any effect on anything, unless it is something sensitive to electronic noise (sound systems, sometimes, or LCD displays.)
Edited by MBakerNH, 18 February 2011 - 08:10 PM.