The Hashtable and SortedList instances returned by this type perform a culture-sensitive, case-insensitive comparison using the current thread's culture (retrieived via CultureInfo.CurrentCulture). If using the Hashtable or SortedList to store identifiers such as file paths, registry keys, and environment variables, or making security decisions based on its contents, construct a Hashtable or SortedList manually using the comparer returned by StringComparer.OrdinalIgnoreCase.
For more information on the correct way to compare strings, see the following article:
New Recommendations for Using Strings in Microsoft .NET 2.0
http://msdn2.microsoft.com/en-us/library/ms973919.aspx