just to re-iterate though, there's a difference here between these USB extenders that use USB cable, which use typically, fixed lengths eg 5m of USB 'daisy chained' between connectors, and the type that use CAT5 cable between the ends, IMO you are better off with the type that use the CAT5.
The other points mentioned above re RF loss etc , yes you will get loss over coax, but there's no RF going down the USB cable, so there is nothing to lose.
Those more technically in the know will correct me but I'd hazard a guess that USB either works or it doesn't ie the signals passing down it might even be digital.
Right, that's me, i'm ducking behind the sofa now.