When you look at the Excel PIA in the object browser in Visual Studio, you will quickly notice what appears to be method centric name calling: a slew of methods with the text “Dummy” in them. There's even an interface called IDummy (implement this interface to indicate you are a dummy).
No, this isn't Excel's way of insulting your intelligence. Everything with “Dummy” in it is a test method that actually has a legitimate purpose and more descriptive names in the debug version of Excel (for example Application.Dummy6 is called Application.DebugMemory in the debug version of Excel), but are renamed to “Dummy” in the retail version of Excel. All these “Dummy” methods (I count 508 of them) actually do something in debug Excel, but in retail Excel they all return E_FAIL--e.g. they don't do anything.
Excel has marked these as “hidden” in the COM typelibrary--and when the PIAs were created, this hidden information is transferred over by TLBIMP using the TypeLibFuncAttribute's FUNCFLAG_FHIDDEN flag. But most object browsers aren't looking for this--so when you view the PIA in the object browser you see these “Dummy” methods regardless of whether the “Show Hidden Members” command in the object browser is selected or deselected. Feature request for reflector or the Visual Studio object browser--look for the TypeLibFuncAttribute's FUNCFLAG_FHIDDEN flag and hide these methods and properties.
You can actually see these Dummy methods in VBA too--but you have to right click on the classes list in object browser and choose “Show Hidden Members” and thhe Dummy methods will appear there too.
This is more noise that is ignorable when browsing the Excel PIA in the object browser.
[Thanks to Adam Nathan!--corrected this post--hidden information is transferred over via the TypeLibFuncAttribute, but most object browsers don't look for this attribute.]