Retrieving a CommandbarPopup in Visual Studio to add buttons has always been tricky. There are incorrect ways to do it:
PRB: Performance problem of DTE.CommandBars[name] for CommandbarPopups in Visual Studio 2010
BTW, I have updated this popular article to avoid that performance problem in VS 2010:
HOWTO: Adding buttons, commandbars and toolbars to Visual Studio .NET from an add-in
and there are correct ones:
HOWTO: Locate commandbars in international versions of Visual Studio.
HOWTO: Get a CommandBar by Guid and Id rather than by name from a Visual Studio add-in.
And now Visual Studio 2010 introduces a new one, which is correct, but doesn't work in international versions of Visual Studio 2005 and 2008:
INFO: menuCommandBar.Controls["Tools"] works in international versions of Visual Studio 2010