Great posting from Jonas about an update regarding the CRM 4.0 plug-in registration tool. Continue reading: http://blogs.msdn.com/jonasd/archive/2008/01/12/access-denied-when-using-pluginregistration-tool.aspx
Plug-in development and registration is a much more powerfull in Microsoft Dynamics CRM 4.0 compared to Microsoft Dynamics CRM 3.0. The Microsoft Dynamics CRM 4.0 SDK ships with two tools helping you to register your plug-ins. Jonas added a smart improvement, he simple added a new property and once checked default credentionals are used when connection to discovery and crm webservice.