  Experience with ASTROVIRTEL, scientific analysis of current large data sets,
and detailed preparation for the truly huge future missions especially GAIA,
provide important lessons for the Astrophysical Virtual Observatory. They
demonstrate that the science cases are impressive, specifically allowing new
thresholds to be crossed. The AVO is more than just faster cheaper better, it
allows the new. The example of use of pre-explosion imaging of supernova to
identify progenitors is used to illustrate some general challenges. Some
non-trivial technical astronomical issues arise, especially astrometry, to
complement the many technical implementation challenges. A critical scientific
lesson is the need to quantify data quality. How are we to ensure the Virtual
Observatory produces top science, and avoids being overwhelmed with mediocre
data?
