@jeff hammond said:

try doing this manually:
[attachment=0:294p5trl]<!-- ia0 -->screen 2012-04-20 at 9.17.04 PM.jpg<!-- ia0 -->[/attachment:294p5trl]

a random line floating in space (not on any particular axis).. then draw a circle perpendicular to it..

with the rotate tool, you can quickly orient the tool to this way.. with the circle, you can't..

This is exactly the situation I use the perpendicular face tool for daily; when I need a circle (or more often a cylinder) to pass through a plane centered on an exact spot, but not perpendicular to the plane itself. Draw a line where I need the cylinder's access, then create a circle perpendicular to the line and push/pull it through.