Using USB redirection with Linux KVM virtualization has been possible since last year, but only today a full-length guide on using this feature has been posted to Linux-KVM.com.
There are two USB redirection modes support: using Red Hat's SPICE protocol or via a TCP server. The TCP solution doesn't depend upon SPICEwhile also supporting other remoting protocols like VNC. For using SPICE there is a GUI-based tool for configuring the USB device redirection while the TCP solution has support built into the virt-manager program.
The Linux-KVM.com guide provides information on how to utilize this USB re-direction with QEMU/KVM.
USB redirection is a nice feature of KVM with many possible use cases. Two that immediately come to mind include backing data from your virtual machine locally or attaching usb devices that provide additional functionality to your guest virtual machine. All this without having physical access to your KVM virtual server.
The big downside to the method explained in this post is having to use multiple management tools to use this feature. In this case it required using virt-manager to configure and start/stop your virtual machine and a separate tool called spicy to perform the usb redirection to your guest.