  We continue our series of papers on open cluster distances with a critical
assessment of the accuracy of main-sequence fitting using isochrones that
employ empirical corrections to the color-temperature relations. We use four
nearby open clusters with multicolor photometry and accurate metallicities and
present a new metallicity for Praesepe ([Fe/H] = +0.11 +/- 0.03) from
high-resolution spectra. The internal precision of distance estimates is about
a factor of 5 better than the case without the color calibrations. After taking
into account all major systematic errors, we obtain distances accurate to about
2%-3% when there exists a good metallicity estimate. Metallicities accurate to
better than 0.1 dex may be obtained from BVIcKs photometry alone. We also
derive a helium abundance for the Pleiades of Y = 0.279 +/- 0.015, which is
equal within the errors to the Sun's initial helium abundance and that of the
Hyades. Our best estimates of distances are (m - M)_0 = 6.33 +/- 0.04, 8.03 +/-
0.04, and 9.61 +/- 0.03 to Praesepe, NGC 2516, and M67, respectively. Our
Pleiades distance at the spectroscopic metallicity, (m - M)_0 = 5.66 +/- 0.01
(internal) +/- 0.05 (systematic), is in excellent agreement with several
geometric distance measurements. We have made calibrated isochrones for -0.3 <=
[Fe/H] <= +0.2 available at http://www.astronomy.ohio-state.edu/iso/ .
