VS2010 Ultimate included IntelliTrace functionality by default. IntelliTrace captures events (e.g. exceptions), and can affect performance of debugging. The typical performance hit is about 5% in the default mode (collection can be increased to
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Read the complete post at http://blogs.iis.net/webdevelopertips/archive/2010/08/19/tip-107-did-you-know-how-to-improve-debugging-performance-for-mvc2-application-in-visual-studio-2010-ultimate.aspx