Synoptic sky surveys are becoming the largest data generators in astronomy,
and they are opening a new research frontier, that touches essentially every
field of astronomy. Opening of the time domain to a systematic exploration will
strengthen our understanding of a number of interesting known phenomena, and
may lead to the discoveries of as yet unknown ones. We describe some lessons
learned over the past decade, and offer some ideas that may guide strategic
considerations in planning and execution of the future synoptic sky surveys.Comment: Invited talk, to appear in proc. IAU SYmp. 285, "New Horizons in Time
Domain Astronomy", eds. E. Griffin et al., Cambridge Univ. Press (2012).
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