Here's the paragraph where he referred to Palestine as a member of the UN, with my own emphasis added:
"This time, we should draw upon the teachings of tolerance that lie at the heart of three great religions that see Jerusalem’s soil as sacred. This time we should reach for what’s best within ourselves. If we do, when we come back here next year, we can have an agreement that will lead to a new member of the United Nations — an independent, sovereign state of Palestine, living in peace with Israel."
So no, what the Palestinians plan to declare on September 23, 2011 is not in line with what Obama declared on September 23, 2010. He did not say a Palestinian state should be declared and admitted into the UN "when we come back here next year" no matter what. He hoped there would be an agreement that would lead to the establishment of Palestine. That is the exact opposite of what the Palestinians have decided to do.
Obama should quote himself in his 2011 UN address. He should emphasize that he called for an agreement bred by Israeli-Palestinian tolerance, not for a move that is counter to Israel's wishes. He can point out that during this year, neither the Palestinian or Israeli leadership acted tolerantly toward the other side. If Obama doesn't do so, Netanyahu should use the quote, not as a reminder to the American administration, which is on Israel's side on this one anyway, but as a reminder to Palestinians and to European countries.