A good bit of the "improving econonmy" is being fueled by all the re-financing of the past 3 years, putting another $300 in everybody's pocket. And given that the average family has some ridiculous number in Credit Card debt (I think greater than $10k), it seems safe to say that every penny people get, they are spending (for the most part). That would be the only reason they would take money out of a 401k, is to spend it. It doesn't make a lot of sense to take money out of a 401K and not spend (ie... transfer to producers) or invest (ie... transfer to producers)....
If the economy is really going to be in trouble in 2008, I would expect to see a major step in the yield curve between 3 year notes and 4 year notes. Is it there?