No human institution can last forever. The US's dominance will end someday.
However, reports of the death of the American empire have been greatly exaggerated. The current financial crisis, while no lark, is being greatly overhyped because of the impending general election. On the terrorism front, whatever you think of Bush policies, there have been no successful terrorist attacks on US domestic targets since 9/11, and Al Qaeda seem to be losing most of the eggs the staked on the Iraq basket. As for low international opinion, being a superpower is a thankless job. Great Britain, Rome, and the rest were all hated in their age, but if you're a superpower, do you really need to be loved by your clients?
The fact is that as things are, the US is needed. I wish it weren't true, but someone has to be the world's policeman. The US, for all its warts and sins, has the best record of any empire in history for intervening with restraint and then pulling out when the mission's over, doing their best to leave the locals in better shape than before.
America will fall someday, but I hope not too soon, and when it finally happens I hope for the sake of the world's people of good will that America's successor is even half as benevolent.
Long Live the Empire!