The historical perspective adds an interesting dimension and indeed the difference between a budget as a plan and a forecast as a prediction is a bit vague. This can all be summarised as a 'guess-estimate' and ultimately that is what budgeting boils down to. It was very interesting to read about the view of Microsoft and its marketing perspective, which would appear to make sense in that particular market and also with a view to market dominance.
The planning aspect that you mention is also an interesting point in terms of the fact that often this activity consumes a large amount of cash for an unknown return, essentially speculation, which is a risk, but as we know, risk and return are very much intuitively related. Also, the strategic aspect of budgeting mentioned and the idea of consistency in budgeting are also relevant. An interesting article by Bento and White (2006) evaluates budgeting from a performance evaluation aspect and this appears to link neatly to many of the themes mentioned in this discussion thread in terms of the importance of participation in the budgeting process from those directly impacted from the budget, although clearly this view will depend heavily on the corporate management culture prevalent within the organization.
Any thoughts?