It has emerged that Microsoft was forced to pull the first incarnation of Windows Vista because a senior executive warned chairman Bill Gates that it was just too hard to work with. Jim Allchin, group VP in charge of Windows, says he told Gates last summer that the Longhorn of the time was quite simply "not going to work" because it was so complex that Microsoft's developers would never be able to make it run properly.
The root of the problem was Microsoft's historical approach to developing software - the so-called 'spaghetti code culture' - where the company's thousands of programmers would each develop their own piece of code and it would then all be stitched together at the end.
As a new approach, a clean solid core code base for Windows was developed that supported adding new features over time much more easily. New tools were also introduced that would reject buggy code. Let's all hope that this makes for a much better final product when we get Vista.