  We have obtained Spitzer Space Telescope IRS 5.5 - 35 micron spectra of 59
main sequence stars that possess IRAS 60 micron excess. The spectra of five
objects possess spectral features that are well-modeled using micron-sized
grains and silicates with crystalline mass fractions 0% - 80%, consistent with
T-Tauri and Herbig AeBe stars. With the exception of eta Crv, these objects are
young with ages <50 Myr. The spectra for the majority of objects are
featureless, suggesting that the emitting grains probably have radii a > 10
micron. We have modeled the excess continua using a continuous disk with a
uniform surface density distribution, expected if Poynting-Robertson and
stellar wind drag are the dominant grain removal processes, and using a single
temperature black body, expected if the dust is located in a narrow ring around
the star. The IRS spectra of many objects are better modeled with a single
temperature black body, suggesting that the disks possess inner holes. The
distribution of grain temperatures, based on our black body fits, peaks at Tgr
= 110 - 130 K. Since the timescale for ice sublimation of micron-sized grains
with Tgr > 110 K is a fraction of a Myr, the lack of warmer material may be
explained if the grains are icy. If planets dynamically clear the central
portions of debris disks, then the frequency of planets around other stars is
probably high. We estimate that the majority of debris disk systems possess
parent body masses, MPB < 1 Mearth. The low inferred parent body masses suggest
that planet formation is an efficient process. (abridged abstract)
