The USB port on the home hub is slow because the home hub only has a very slow processor, and the USB port is given a very low priority.
The home hubs 1, 1.5, and 2 are the worst, but I believe the home hub 3 is slightly better.
The best option is to use a proper NAS device, which plugs into an Ethernet port.
Cheers so I plug one of these into the back of my Home Hub and that will be quicker?
Yes, that is what a NAS is for. I have a Zyxel NSA210 NAS which has a 1TB disk inside, which holds all of our music and video, and can stream to any device on the network.
I have found it 100% reliable, and never disappears off the network.
This has been superceded by the Zyxel NSA 310, which has a much faster file transfer rate.
There is a picture of my home network here.