I'm wondering what kind of misalingment in a circular saw base plate
is "acceptable".

Mine is a right-blade depth-adjustable (Porter Cable 447K), and at
some depth settings the rear of the saw blade is about 1mm closer to
the farther (left) edge than the front of the saw. If I try to do
anything like this:
http://www.womeninwoodworking.com/ti...ingpoints7.cfm
then the saw will either track away from the guide or the blade will
score the workpiece about 1mm more than I intend to cut. (And the
misalignment varies w.r.t. depth as well!)

(The front is 5in from the edge of the kerf dead-on, as touted by the
specs.)