Two customers (so far) wanted to know how to increase the duration of taskbar balloon notifications on Windows Vista. (By the way, I gave the answer some time ago.) They claimed that on Windows XP, they were using the registry key HKEY_CURRENT_USER\Software\Microsoft\Windows\Current­Version\Explorer\Tray­Notify, setting the value Balloon­Tip to a REG_DWORD specifying the number of seconds the balloon should appear. They wanted to know if this still worked in Vista. Heck, it didn’t work even in Windows XP! That undocumented registry key actually controls whether the Windows XP taskbar should show the “To see the hidden icons, click this button” tip. It has nothing to do with how long the balloon stays on the screen. A quick Web search suggests that that particular setting has reached cult status, with everybody saying that the setting controls balloon duration, and nobody actually testing it. It’s just a matter of faith. Even the sometimes-suggested trick of putting the registry key name in MSDN so searches can find it and direct users to the correct method wouldn’t have helped, because this was the wrong registry key to begin with.

(Remember, the answer is in the linked article.)