Um, guys, if I'm reading the original post correctly, he wasn't talking about extending the length of the handle, but about adding a standard extension between the torque wrench and the socket.
In this case, yes, you will lose some small amount of the applied torque, because some of the torque will go into the twisting of the extension, because it will basically act like a torsion spring. The general rule of thumb I've always followed is keep the distance from the tq wrench to the fastener as short as possible, and when you must use an extension, raise your applied torque a little bit; usually I'll lean toward the higher end of the spec of whatever I'm tightening when that is the case.
