I can't speak for Nagasaki as I have never been there, but I have been to Hiroshima multiple times and I have friends there. And let me tell you: there are a lot of American people living in Hiroshima. If the Japanese there became angry every time they saw an American, they would be angry almost everyday. And we are talking about just residents, if we add in all the tourists, then they would be angry nearly all of the time. That doesn't seem like a healthy way to live.
There is a book I always suggest everyone to read. Letters from the End of the World: A Firsthand Account of the Bombing of Hiroshima by Toyofumi Ogura. He survived the bombing. His wife wasn't so lucky, leaving him a single father. Despite all, he writes that he wasn't angry at America for the a-bomb but rather was angry at the military government which got his country involved in such a stupid war. Many older people I talk to express a similar attitude.
No one, American or Japanese, is happy about the deaths and destruction the a-bombs caused. It seemed like the necessary choice to prevent even more deaths*, but that doesn't mean we are happy about it. At any rate, it was long ago and the prevailing emotion is more of sadness not anger. Sadness there was war, sadness there was death, sadness there is still war. Of all the cities in Japan, Hiroshima and Nagasaki are the most dedicated to pacifism.
Also, after the war America came in to help rebuild the country. This and the general good actions by the soldiers left a good impression and a general good feeling towards America.
But really, most people today... except for Aug 6th at 815 am and Aug 9th at 11:02 when many places will have an announcement asking for a moment of silence, they never even thing about it. Why would they? It happened 70 years ago. Most people have moved on.
There are of course people who are still angry about the war. I have a feeling most people still mad abut the war are people who were born after the war and just want something to be mad about. When I first arrived in the country some years ago I was confronted by an angry middle aged man who demanded "Why did you bomb Hiroshima??". Not really sure how to react, I simply replied "Why did you invade China." That shut him up. In all my years here that remains the only time I have ever seen any anger about the issue