With all of the VS 2005 DTE methods returning System.Object rather than
x.x.x.CommandBars, I assumed this was for backwards compatibility.
However, I'm getting an InvalidCastException on the following lines of
code in 2005 when CommandBars is from the Microsoft.Office.Core
namespace in the office interop assembly:

// TODO discrepancy 2003/2005 office or vs command bars assembly
CommandBars commandBars = (CommandBars)this.Application.CommandBars;

I reflected the assembly and saw that the COM GUIDs for the CommandBars
classes are different ... Does this mean I'm out of luck in trying to
use a single codebase for both 2003 and 2005?  This line of code is
only one of hundreds that I would have to conditionally compile two
versions of!

Jake