usb2 is no where close to the bus speed of pcmcia!
another issue to consider is that MOST usb2 controllers do not run at its highest speed.
did you know that there are 3 speeds for usb2? 1.5mbs, 11mbs, and 480mbs. they are labeled as low, full and high speed respectively...most of them(controllers and devices) are NOT "high speed". also even the highest speed of usb2 is only a theoretical peak speed...standard firewire has a higher _average_ throughput than the fastest usb2's _average_ throughput.
not saying usb/usb2 is bad, it isn't, but its more marketing than actual proven performance.
pcmcia is even faster and more stable than firewire400/firewire800....external scsi drives for laptops are based on the pcmcia interface