With the new Vista Operating System, Microsoft has once again proven that is stands behind it's traditional fat-client business model. Considering that Windows and Office account for more than 60% of the companies revenue, I suppose it make sense to stick with what has worked in the past. Only problem is that ultimately it's the customer that suffers in the end with the hefty annual fees for the upgrades.
I am still a huge believer in the Software as a Service model simply because of the benefits that the customer immediately realizes. Low risk, low cost, zero implementation.