  The potential of the Sloan Digital Sky Survey for wide-field variability
studies is illustrated using multi-epoch observations for 3,000,000 point
sources observed in 700 deg2 of sky, with time spans ranging from 3 hours to 3
years. These repeated observations of the same sources demonstrate that SDSS
delivers ~0.02 mag photometry with well behaved and understood errors. We show
that quasars dominate optically faint (r > 18) point sources that are variable
on time scales longer than a few months, while for shorter time scales, and at
bright magnitudes, most variable sources are stars.
