Steve Scarich
Thanks for all the good feedback. Here's a summary of opinions:
-safest thing to do is toss the fork. You never know how it got damaged or where stresses have occurred.
-since the crack is at the top of the excess steerer, if you're cheap, and willing to take a small risk, several people recommended cutting 3mm below the end of the crack (which might not be visible from the outside), using a carbon specific blade. Sand it smooth after cutting.
-several people advised that you always have at least one spacer above AND below the stem; seems to help prevent cracks at top.
Steve Scarich