  Rest-frame far-ultraviolet (FUV) luminosities form the `backbone' of our
understanding of star formation at all cosmic epochs. These luminosities are
typically corrected for dust by assuming that the tight relationship between
the UV spectral slopes and the FUV attenuations of starburst galaxies applies
for all star-forming galaxies. Data from seven independent UV experiments
demonstrates that quiescent, `normal' star-forming galaxies deviate
substantially from the starburst galaxy spectral slope-attenuation correlation,
in the sense that normal galaxies are redder than starbursts. Spatially
resolved data for the Large Magellanic Cloud suggests that dust geometry and
properties, coupled with a small contribution from older stellar populations,
cause deviations from the starburst galaxy spectral slope-attenuation
correlation. Folding in data for starbursts and ultra-luminous infrared
galaxies, it is clear that neither rest-frame UV-optical colors nor UV/H-alpha
significantly help in constraining the UV attenuation. These results argue that
the estimation of SF rates from rest-frame UV and optical data alone is 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.
