Claudio Silva has a post covering Reporting Services Powershell cmdlets:
In this post I will share with you the request and how I have automated it saving a lot of time. Just to keep you interested, I went from 23 and a half minutes to 3 (your mileage may vary depending on the number of objects/actions that you need to do).
The request
Create new folder “FolderB”
We need to deploy a copy of the reports and data source to a new folder (“FolderB”). You should get the existing ones from the folder “FolderA” on the same server.
Then you have to change the datasource to point to the database “dbRS” with the login “ReportingUser”
Finally we need to change the data source for each report to match the new datasource pointing to database “dbRS” created on last step.
Click through for the code. Claudio even has a one-minute video showing his work in action.