Here's a couple resources (some older and some newer) that should be useful for those of you looking to protect your base system from accidental or malicious modification.

Developing as Non-Admin [in Visual Studio.NET]: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dv_vstechart/html/tchDevelopingSoftwareInVisualStudioNETWithNon-AdministrativePrivileges.asp

Aaron Margosis' Non-Admin Blog: http://blogs.msdn.com/Aaron_Margosis/

Updated: Fixed newlines