When you create a shared data source in the BIDS tool, the file gets the .rds extension. When the shared data source is deployed to Sharepoint 2010, it gets the .rsds extension.
Hence, lets say your source control went belly up, and you had to recreate a blank SSRS solution from scratch, you could in theory download a copy of the rsds files from Sharepoint 2010 into the new solution framework. However you may get an error “There is an error in XML document (2,2) (System.Xml)”.
This is due to the schema differences between the RDS and RSDS files as outlined here Create and Manage Data Sources in Int Mode.
Workaround is to recreate the data sources manually ensuring the same name and properties are set. The reason is outlined in the reference below which can be summarised as “When you publish a shared data source (.rds) file to a SharePoint site, this changes the data source file to an .rsds file name extension. The .rsds file cannot be saved locally from a SharePoint site and imported into an existing Reporting Services project. Shared data sources with file name extensions .rds and .rsds are not interchangeable”.
Sorry guys – don’t shoot the messenger – see here for further details Deploying Models and Shared Data Sources to Sharepoint.
If you cannot remember the specific names and details of the data sources and don’t have access to trawl through the Sharepoint Site for them, then you could refer to your Pragmatic Works BI Documenter end to end solution documentation (if you are lucky enough to have it installed, and have daily solution snapshots running).