To be a useful research tool, MOM needs to be easily configurable in many different ways. Also of importance is access to a large number of parameterizations for intercomparisons within the framework of one model. Using preprocessor ``ifdefs'' gives this flexibility. However, they must be used wisely. Indiscriminant use of preprocessor ``ifdefs'' can lead to a tangled mess of limited usefullness. With time, more and more constructs within MOM will be replaced by their Fortran 90 counterparts which should allow for even greater flexibility.