From http://library.uchastings.edu/library/Legal%20Research/Research%20Guides/treaties.htm (bold is mine)

Once in force, treaties are binding upon all parties signatory to it. Article VI of the U.S. Constitution declares treaties to which the U.S. is a party to be the "supreme law of the land".

Now, the UN charter is one of the many treaties signed by the US, you can find it listed here, in 1945:
http://en.wikipedia.org/wiki/List_of_United_States_treaties

Then you have from http://en.wikipedia.org/wiki/UN_Charter (bold is mine)

As a Charter it is a constituent treaty, and all signatories are bound by its articles. Furthermore, it explicitly says that the Charter trumps all other treaty obligations. It was ratified by the United States on August 8, 1945, making that nation the third, after Nicaragua and El Salvador, to join the new international organization.


>>Besides, who's to decide whether each "Security Council resolution is a good one, based on sound reasoning"? You and I? We've already shown to each other that our ideas of sound reasoning differ. Since we couldn't possibly agree on that, we have delegated that task to the world's parliament, the UN.
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>The United Nations is now the world's parliament? That is an interesting perspective. I am fairly certain that whatever "laws" the United Nations passes, I as a citizen of the United States am not subject to them. I am subject to the laws of the United States, however.