I highly doubt it
I'm not sure if anyone else has thought of this, but you can't boot your computer from a USB hard drive if anything happened to your main hard drive, making the only option booting from a DVD drive. Also, what if you want to boot from Windows? I know it's possible with only one hard drive, but complex and limiting in space as well as making that one hard drive susceptible to viruses and spyware, slowing the entire computer down.
You'd also be compromising speed to switch soley to USB, Firewire has a higher sustainable speed than USB does.
I'm not sure if anyone else has thought of this, but you can't boot your computer from a USB hard drive if anything happened to your main hard drive, making the only option booting from a DVD drive. Also, what if you want to boot from Windows? I know it's possible with only one hard drive, but complex and limiting in space as well as making that one hard drive susceptible to viruses and spyware, slowing the entire computer down.
You'd also be compromising speed to switch soley to USB, Firewire has a higher sustainable speed than USB does.