  This paper reports on an all-sky search for periodic gravitational waves from
sources such as deformed isolated rapidly-spinning neutron stars. The analysis
uses 840 hours of data from 66 days of the fifth LIGO science run (S5). The
data was searched for quasi-monochromatic waves with frequencies f in the range
from 50 Hz to 1500 Hz, with a linear frequency drift \dot{f} (measured at the
solar system barycenter) in the range -f/\tau < \dot{f} < 0.1 f/\tau, for a
minimum spin-down age \tau of 1000 years for signals below 400 Hz and 8000
years above 400 Hz. The main computational work of the search was distributed
over approximately 100000 computers volunteered by the general public. This
large computing power allowed the use of a relatively long coherent integration
time of 30 hours while searching a large parameter space. This search extends
Einstein@Home's previous search in LIGO S4 data to about three times better
sensitivity. No statistically significant signals were found. In the 125 Hz to
225 Hz band, more than 90% of sources with dimensionless gravitational-wave
strain tensor amplitude greater than 3e-24 would have been detected.
