With the new Feature Pack booting an Xpe device from USB 2.0 (1.1 is not supported) will be a piece of cake. Just add the new USB component, run dependency check and disable some of the older dependencies.
I was able to boot my Dell Lattitude D800 from a PNY 1 GB USB stick right away.
But please, be aware that this is not as fast as booting from a CF card connected to the IDE controller (ideally fixed CF card, with DMA support).
USB Boot certainly is a great enabler for quite a few interesting change management and maintenance scenarios.
Thefore, give it a try! 😉