I believe that Firewire is still the preferred connection method, even with the Intel Macs.
Although, on paper, the USB 2 has the edge in speed over Firewire 400, that speed is seldom achieved. USB is processor intensive while Firewire does not rely on the processor to control the flow of data.
(Heads up for flack)
Currently, if I remember correctly, you cannot boot the Mac from a USB device, which is another tick in the minus column for USB.
... just got curious as I sit here looking at the external hard drive blink while it talks with my G4 iBook... the old G4 and G5 models supposedly worked best when they connected to external peripherals using firewire (what is it's official designation... ieee 1394?).
Anyway... is the preference for firewire connectivity continued with the new mac-intel machines?