I made some changes to my Team Foundation Server builds, and wanted to check out the nice new reports.. only to see they havn't been updated yet.
Kevin Castle has a good overview of this, explaining that the data warehouse does not update itself right away. There is a web service he suggests that you call, although the manual web address for me is different (SP1 maybe?)
http://localhost:8080/Warehouse/v1.0/warehousecontroller.asmx?op=Run