I found a bug in the Microsoft Report Viewer 2005 control. When used in LocalMode in an application that does not have a strongName signature, the reportViewer control saves temporary files to IsolatedStorage folder and does not ever delete the temporary files that it creates. So the result of this is that it takes up a lot of harddrive space, about 240k per page of the report. And when a report has 900 pages, this is a problemo. The problem is solved simply by making sure that your application has a strong name key (see the “signing” tab of project properties).
Nevertheless, this untidy habit of not cleaning up after itself caused me a lot of problems, several customer servers where this application is installed almost ran out of hard drive space because of this bug. Not good!