I believe the US economy is slowing along with the economies of the rest of the world. Austerity across the world will weigh on economic growth along with the end of the inventory rebuild and the end of QE II. The decoupling argument is wishful thinking at best.
A slowdown will only effect markets if it effects corporate profits. Thus far corporate profits have held up but at some point they will take a hit. The extent of the slowdown will dictate the effect on corporate profits. I am uncertain if we will be able to muddle through or if it will be worse.
I don't believe paying up for stocks is a good idea in the current environment. At the same time I don't believe the bears will be rewarded until corporate profits are effected. I believe the best course of action is to buy pessimism and sell optimism.