SSRS Overwrite Datasources - Avoid the Headache of Reports Not Updating

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=2908860&SiteID=1
In order to avoid complete headache, consider these settings.

Right click your project name in solution explorer of BIS.

Set overwrite datasources to true. Click configuration manager. Check the checkboxes for build and deploy on both debug configuration and production configuration.
Retype the target server url after clicking ok to be http://localhost/reportserver.
Make sure the deploy folder is the correct folder (it may reset this). Rebuild and deploy the report.

As a side-note, SSRS 2005 caches reports. It will keep a .rdl.data cache file around which caches the dataset instead of always reexecuting dataset queries.
Try closing VS, deleting the .rdl.data file, and reopening again?