This week, the State Department issued its annual report on terrorist activity, available at http://www.state.gov/documents/organization/122599.pdf, which includes "An Academic's Perspective on Open Source Event Data," written by START Director Gary LaFree (page 351).
A more comprehensive piece by Gary LaFree is included in the National Counterterrorism Center's (NCTC's) companion report at http://www.fbi.gov/stats-services/publications/terror_08.pdff (starting page 72).