2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/163289This is an overview of math.AG/0310186, math.AG/0309290, math.AG/0501247, math.AG/0401002 and math.AG/0504584 written for the Proceedings of the AMS Meeting on Algebraic Geometry, Seattle, 2005.29 pages, LaTeX2e. Final version to be published by the AMSAlgebraic Geometrytext