The MSigDB Perturbation  ontology contains gene sets that represent gene expression signatures of genetic and chemical perturbations. A number of these gene sets come in pairs: an xxx_UP (xxx_DN) gene set representing genes induced (repressed) by the perturbation.
Statistics can now be found in the footers of each table in the GREAT web output.
All ontology data was downloaded and built between Oct 14, 2011 and Feb 18, 2012.
GREAT v1.8 MSigDB Perturbation statistics are available here.
GREAT v1.2 MSigDB Perturbation statistics are available here.
Subramanian, A., et al. Gene set enrichment analysis: a knowledge-based approach for interpreting genome-wide expression profiles, Proc Natl Acad Sci U S A. 2005 Oct 25; 102(43):15545-50.