FireWire is better for connecting external hard drives than USB. FireWire is better for connecting video devices than USB. FireWire allows one Macs to be mounted by another Mac as a remote drive using Target Disk Mode; USB does not.
Still, the direction has been inexorable. The first generation iPods could be connected to Macs (or PCs) using either USB or FireWire. Apple dropped that feature many years ago, unfortunately.
So, no FireWire on the new 13" MacBook or MacBook Air. No FireWire 400 (the common type) on the new 15" and 17" MacBook Pro models, only FireWire 800.
What next? I think it's safe to assume that updates to the Mac Mini, iMac and Mac Pro will lack FireWire 400 ports, and might not even have FireWire 800 ports (which are backwards-compatible with FireWire 400). Not having any FireWire at all is unfortunately, to say the least.
Consider the widely reported rumor that an update of the Mac Mini might be based on the 32-bit Intel Atom processor, instead of the 32/64-bit Intel Core 2 Duo processor. The chipsets available for the Atom don't support FireWire in any incarnation.
Now, it's possible that the rumors are wrong... but if I were you, I'd not count on having any FireWire ports on new Apple hardware, except for the most high-end systems, like Mac Pro or maybe MacBook Pro. Moving forward, I wouldn't bet on FireWire 800 surviving on the high-end Macs beyond the next year or two.