The obvious answers are:
1) Airport security is tighter. National security is a higher priority and it is tighter in general.
2) Prejudice towards Muslims and anyone who is or appears to be of Middle Eastern descent has increased.
3) Americans have become more patriotic. Proud and protective of our country. Being American in and of itself has become a unifying commonality.
4) Ironic in the presence of #3, general prejudice (overall, not targeted) seems to have reduced. We did vote Obama in after all (or maybe that's unrelated).
5) Education and knowledge of the Muslim religion, and it's different sects has increased.
6) Acknowledgment and appreciation of the work our military, police and fireman do has increased.
7) We (Americans) have a greater appreciation of the (relative) peace and civility that we usually take for granted in our country. There is no war on our soil and we are not as poverty stricken as other (smaller and third world) countries.
8) We appreciate our loved ones more. 9/11 was like having the rug snatched from under us. It was horrifying and so, so many people were lost. It proves that you never know what is going to happen, and no one is promised a new day.
9) We learned that our country has it's vulnerabilities, but we also have great strength, hope and optimism. We have showed a strong recovery from that tragedy, and we're still not done with the after effects, however we continue to forge ahead.