  Rest-frame far-ultraviolet (FUV) luminosities form the `backbone' of our
understanding of star formation at all cosmic epochs. FUV luminosities are
typically corrected for dust by assuming that extinction indicators which have
been calibrated for local starbursting galaxies apply to all star-forming
galaxies. I present evidence that `normal' star-forming galaxies have
systematically redder UV/optical colors than starbursting galaxies at a given
FUV extinction. This is attributed to differences in star/dust geometry,
coupled with a small contribution from older stellar populations. Folding in
data for starbursts and ultra-luminous infrared galaxies, I conclude that SF
rates from rest-frame UV and optical data alone are subject to large (factors
of at least a few) systematic uncertainties because of dust, which cannot be
reliably corrected for using only UV/optical diagnostics.
