Unfortunately, finding the right hardware is not easy. Many motherboards default to USB,CD,HD (unless changed by the user) USB can have sevral names (such as LS120). It would be great if motherboard companies would increase support for USB booting (I contacted XFX, who made mine about USB booting, they just ignored me).
Another problem with USB distros is space, flonix would certainly not qualify as anymore than an internet client.
Someone should really make a simple distro with lots of hw support, XPde, abiword, firebird, gnumeric, SciTE, maybe a game or two and that's it, no more extra stuff. That would probably work best for a USB distro.