We've recently been experiencing an SSRS (SQL Server 2008) report displayed in an ASP.NET web application using the ReportViewer control (Microsoft.ReportViewer.WebForms, Version=9.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a) hanging when rendering a report with over 100 rows and causing Internet Explorer (6, 7, 8) to use 100% (of one core) of CPU.
The report renders quickly in Firefox (and doesn't use high CPU).