My telegraphic opinion re. the prospects of capitalism is that capitalism is a bundle. We need to un-bundle it a bit -- to the extent most people do in their minds and attitudes, sometimes consciously, sometimes not.
The basis of historical (or actually-existing) capitalism is a shifting, complicated mixture of (1) capitalist accumulation and (2) extra-economic appropriation. In turn, capitalist accumulation is based on (3) markets and (4) wealth inequality. [If it weren't obvious, I'd argue that extra-economic appropriation is also likely to be induced by much inequality. So, inequality sucks through (1) and (2).]
Now, the bases of historical capitalism are to be distinguished from its main consequences: (5) the exploitation of labor, (6) the social alienation and conflictive exacerbation of human differences, and (7) the destruction of the natural environment -- which together amount to (7) the degradation and destruction of human and perhaps all life on earth.
As far as the bases, two of them are in the crosshairs: (4) inequality and (above all) (2) extra-economic exploitation. I don't mean that they are about to be abolished or reduced to marginal phenomena in human history. Not yet. The political movement required to abolish or minimize them is not here yet. But it will emerge, if it's not already emerging. Large masses of people in the whole world are starting to look at (2) and (to a lesser extent) (4) as aberrations, unacceptable in a civilized global society. That's why I believe that those two aspects of historical capitalism are fried. It's just a matter of time. Only a huge catastrophe could devolve legitimacy to (2) and (4).
On the other hand, markets are safe for the time being. I mean, even Marx considered trade per se as a form of cooperation -- sure a form of cooperation in which the social division of labor takes place behind the backs of the producers, but cooperation nonetheless. Markets only entail the possibility, but not the necessity of capitalist crises -- Marx also wrote wisely. It's the social conditions on which markets operate that make the difference -- especially inequality. In the struggle to erode the bases of capitalism -- It's the inequality, stupid!
If we regard economic theory as the highest form of ideological rationalization of historical capitalism, then inequality is its Achilles Heel. There's nothing (absolutely nothing!) in the robust elements of economic theory that can justify inequality. That's why the economists would rather shift the focus to markets.
Regarding (6), specifically global warming and its quickly growing effects, the best strategy is to leverage the popular discontent against imperialism and inequality to push for a just distribution of the damage.
Finally, with regards to the economic situation in the U.S., I think that even an ideological hack like Greenspan admits that the weight of the U.S. in the world economy is very likely to continue to shrink. A serious recession would accelerate that fall, which is always relative. The U.S. has still a large, resilient economy. Its resilience is based largely on the fragmentation of the working people. I used to think that there was, among the bourgeois elites in the country, an element that could make it possible for a positive-sum economy to be sustained. But now I'm much more skeptical of that. The game is a negative-sum one. The elites are ideologically much narrower and vicious than I used to think.
But who knows, with a Bloomberg-Hagel ticket I may have to change my view. For the U.S. left, the task in the short-run is still to cohere the large but diffuse discontent against (2) (read here Out of Iraq and Foreign policy reform) and (4) (read here Universal health care, Fair preventive public action against the effects of global warming, and Repeal of the tax-cuts for the super-rich). In the long run, the task is still communism.