You may find this problem being arised by your customers. You can find the description in the KB: http://support.microsoft.com/kb/953457/en-us
As you can read in the BCL recommendations at http://blogs.msdn.com/bclteam/archive/2005/06/01/424012.aspx
DO: Use ToUpperInvariant rather than ToLowerInvariant when normalizing strings for comparison.
The problem here is that the key is used as the value too, so navigation control shows uppercase title sites.