From the user point of view, it's yet another hole to plug things into.
The bandwidth is large enough to encompass a number of slow to medium
speed devices so there is hope that it will eliminate some of the
other holes.  Practice seems to be that it is replacing a PS/2 keyboard
and PS/2 mouse hole in some but not all machines.  I expect that it'll
keep going and replace the serial ports too.  As such I'm a happy
camper.

 From an implementation point of view, the bus is beyong baroque and
manufacturers have been slow to release the protocols needed to
drive devices on the USB.  That means that, once again, we'll be
behind the curve as we try to pry details out to get working the
devices that we had working before USB.