If you are running Windows XP Service Pack 3, and also have Google Desktop installed, you may find that every time you reboot, the Quick Launch Toolbar, on the Windows Task bar, vanishes. I found that disabling the Google Desktop toolbar (right click on a blank area of your taskbar, Toolbars > uncheck 'Google Desktop') corrects this issue. If you do not have Google Desktop installed, try this solution:

1. In Registry Editor (Start > Run... > regedit), navigate to:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon

2. Find the "Userinit" key
3. it probably contains:

%system32%\wsaupdater.exe,

where %system32% represents the path to the System32 folder. For example, C:\Windows\System32

4. Instead of wsaupdater.exe, the data should contain userinit.exe,. Using the example above, change it to:

C:\Windows\System32\userinit.exe,

Do not forget to add the comma at the end!!!

5. Close the Registry Editor and reboot your computer.