If you're the only one who uses your computer and you're not on a network, you can reduce the clutter on the Start menu by removing the Log Off item from the Start menu. To do so, launch the Registry Editor by typing Regedit in the Run dialog box and open the HKEY_CURRENT_USER\\Software\Microsoft\Windows\ CurrentVersion\Policies\Explorer folder.

Next, pull down the Edit menu, select the New | DWORD Value command, and name the value NoLogOff. Now, press "Enter" twice to enable the new name and to open the "Edit DWORD Value" dialog box. Once the "Edit DWORD Value" dialog box appears, type 1 in the Value Data text box, click OK and close the Registry Editor. Your last step is to reboot, there is also an alternate and faster way of doing this on this page.

You could do this the easy way and get Tweaki(there is a link to that in my list of "Things a computer should have".