SP1 includes a variety of improvements to the inital product release. Documentation for this release is provided in the SP1readme_lang.htm file which can be downloaded below or found in the Reporting Services installation directory after Setup is complete.
For the complete article, go to: http://www.microsoft.com/downloads/details.aspx?familyid=580febf7-2972-40e7-bccf-6cd90ac2f464&displaylang=en