We had an interesting request last week from the business. They were concerned that some users were exporting data to excel and 
running the business from excel, which was quite surprising as I distinctly 
remember making sure that nobody had permissions to do so.
Turns out that they were exporting the reports which are old fashioned SSRS reports.
So we decided to disable export to all formats but PDF.
Look for the 
rsreportserver.config file and change the Render section to this (in essence add Visible="false" to any extension you don't want to allow to be exported):
<Render>
<Extension Name="XML" Type="Microsoft.ReportingServices.Rendering.DataRenderer.XmlDataReport,Microsoft.ReportingServices.DataRendering" Visible="false"/>
<Extension Name="NULL" Type="Microsoft.ReportingServices.Rendering.NullRenderer.NullReport,Microsoft.ReportingServices.NullRendering" Visible="false"/>
<Extension Name="CSV" Type="Microsoft.ReportingServices.Rendering.DataRenderer.CsvReport,Microsoft.ReportingServices.DataRendering" Visible="false"/>
<Extension Name="ATOM" Type="Microsoft.ReportingServices.Rendering.DataRenderer.AtomDataReport,Microsoft.ReportingServices.DataRendering" Visible="false"/>
<Extension Name="PDF" Type="Microsoft.ReportingServices.Rendering.ImageRenderer.PDFRenderer,Microsoft.ReportingServices.ImageRendering"/>
<Extension Name="RGDI" Type="Microsoft.ReportingServices.Rendering.ImageRenderer.RGDIRenderer,Microsoft.ReportingServices.ImageRendering" Visible="false"/>
<Extension Name="HTML4.0" Type="Microsoft.ReportingServices.Rendering.HtmlRenderer.Html40RenderingExtension,Microsoft.ReportingServices.HtmlRendering" Visible="false"/>
<Extension Name="MHTML" Type="Microsoft.ReportingServices.Rendering.HtmlRenderer.MHtmlRenderingExtension,Microsoft.ReportingServices.HtmlRendering" Visible="false"/>
<Extension Name="EXCEL" Type="Microsoft.ReportingServices.Rendering.ExcelRenderer.ExcelRenderer,Microsoft.ReportingServices.ExcelRendering" Visible="false"/>
<Extension Name="RPL" Type="Microsoft.ReportingServices.Rendering.RPLRendering.RPLRenderer,Microsoft.ReportingServices.RPLRendering" Visible="false" LogAllExecutionRequests="false"/>
<Extension Name="IMAGE" Type="Microsoft.ReportingServices.Rendering.ImageRenderer.ImageRenderer,Microsoft.ReportingServices.ImageRendering" Visible="false"/>
<Extension Name="WORD" Type="Microsoft.ReportingServices.Rendering.WordRenderer.WordDocumentRenderer,Microsoft.ReportingServices.WordRendering" Visible="false"/>
</Render>