  The string duality revolution calls into question virtually all of the
working assumptions of string model builders. A number of difficult questions
arise. I use fractional charge as an example of a criterion which one would
hope is robust beyond the weak coupling heterotic limit. Talk given at the 5th
International Workshop on Supersymmetry and Unification of Fundamental
Interactions (SUSY-96), University of Maryland, College Park, May 29 - June 1,
1996.
