Something we found yesterday, which, in retrospect kinda almost sorta makes sense…we generally run our Reporting Services instances in a multi-tier format, i.e., web server running the website, app server running the RS web portions (occasionally, this also runs on the web server), and the database doing its thing. Well, after upgrading the web/app site to SP3, our datasource stopped working. Turns out that because the credentials are stored securely in the database, the SP3 upgrade invalidates that encryption and sets the datasource to Windows Integrated Security by default. That was a headache.