Very high percentage? I don't buy that, considering most of the systems I can see on bestbuy.com lack USB 3.0 ports. Sure, a handful of motherboard makers are implementing it, but odds are it won't see mass deployment until Intel gets around to adding it to their core chipsets.
Yeah, it will be nice when it gets here, but the Mac side is not behind on this one. It's a slow start across the industry right now.
I will agree this will probably kill Firewire completely at this point. I don't see many vendors sticking to it for newer products in any field. USB 3 at least brings along the good parts of Firewire in the base spec, like device-initiated communications and a non broadcast based messaging setup.