All right, as a half-black, half-white man who considers himself "black", let me answer the questions put forth, as how they relate to me.
Why do I consider myself black? It mainly has to do with how I look. I have brown skin and brown eyes. I look more black than I do white. It also has to do with how I have been treated by people in my life. I have been the victim of racism and discriminated against by people that made it abundantly clear that I was not white. It was just a personal choice that I made. I assume that Obama and others that consider him black, feel the same way.
I am in NO way denying my white side. I was raised by my mother, who is white, and I love her to death. She and my father had nothing but problems being a mixed couple in the 60's. His family didn't like her and her family didn't like him. She told me that they even lived in their car briefly as they weren't welcome in either parents homes. Unfortunately due to their youth and the rigors of being an interracial couple, they broke up soon after I was born. I've only met my real father a couple of times.
Unfortunately, I have also felt racism on the part of blacks towards me. I was raised by my mother, so I have more white mannerisms than black ones. I HATE the whole "ghetto-fabulous" craze that makes blacks look ignorant. I love being mixed, but it did make growing up difficult. But what doesn't kill you makes you stronger.
Obama is considered black, because he sure isn't white. As Highfigh himself said, Obama might not have won the election if he was 100% black. This statement illustrates that racism is still prevalent in this country. So whether you like it or not, race was a factor in the last election. I see Obama's election as a positive, as it seems like we are moving in the right direction. Perhaps some day race will not be an issue in politics, but we are not there yet.