Consider the following scenario:
- You have a computer that is running windows 7 or Windows Server 2008 R2.
- You set a solid color as the desktop background.
- The Desktop Window Manager Session Manager service is running.
- You log on to the computer locally.
So if you like a plain desktop, its not necessarily what Microsoft thought was the case. One of the reasons why you might face the issue of delayed logons can be that you have chosen a solid color for your desktop.
see the following link for more details and a hotfix.