  We present a line-by-line differential analysis of a sample of 16 planet
hosting stars and 68 comparison stars using high resolution, high
signal-to-noise ratio spectra gathered using Keck. We obtained accurate stellar
parameters and high-precision relative chemical abundances with average
uncertainties in \teff, \logg, [Fe/H] and [X/H] of 15 K, 0.034 [cgs], 0.012 dex
and 0.025 dex, respectively. For each planet host, we identify a set of
comparison stars and examine the abundance differences (corrected for Galactic
chemical evolution effect) as a function of the dust condensation temperature,
\tcond, of the individual elements. While we confirm that the Sun exhibits a
negative trend between abundance and \tcond, we also confirm that the remaining
planet hosts exhibit a variety of abundance $-$ \tcond\ trends with no clear
dependence upon age, metallicity or \teff. The diversity in the chemical
compositions of planet hosting stars relative to their comparison stars could
reflect the range of possible planet-induced effects present in these planet
hosts, from the sequestration of rocky material (refractory poor), to the
possible ingestion of planets (refractory rich). Other possible explanations
include differences in the timescale, efficiency and degree of planet formation
or inhomogeneous chemical evolution. Although we do not find an unambiguous
chemical signature of planet formation among our sample, the high-precision
chemical abundances of the host stars are essential for constraining the
composition and structure of their exoplanets.
