A few words of caution. The report was not based on the same high standards of a judicial investigation, it was intended to provide a broad mapping of he most serious human rights abuses between 1993 and 2003.
Indeed, the report says that an international court will have to be the final arbiter whether the RPA/AFDL did commit acts of genocide. Verbatim: "The systematic and widespread attacks described in this report, which targeted very large numbers of Rwandan Hutu refugees and members of the Hutu civilian population, resulting in their death, reveal a number of damning elements that, if they were proven before a competent court, could be classified as crimes of genocide."
Nonetheless, it was their mandate to documents crimes of genocide, and they were rigorous: In total, the team gathered evidence on 600 incidents of violence (not just on the genocide allegations). Their standard was two independent sources for each incident. They interviewed 1,280 witnesses and gathered 1,500 documents. Many of the reports of killings of Congolese and Rwandan Hutu civilians were corroborated by eyewitnesses. While we always knew that there had been large massacres of Hutu refugees in the Congo, this is the first rigorous investigation, and the first time an international body has thrown its weight behind charges of genocide.
Another word of caution: This is the preliminary draft. The report is due to be released on Monday, but it has been leaked, I gather because the Secretary General Ban Ki Moon has pressed for the charges of "acts of genocide by the RPA/AFDL" to be removed. The Rwandan government has reportedly threatened to withdraw its troops from the AU mission in Darfur and I have even heard that they will withdraw from the UN all together, becoming "associate" or "observer" states. I imagine that it is to prevent such editing that the report was finally leaked.