Will Obama be able to comment on certain black issues in a way that a white president would not be able to. What might those issues be? Why shouldn't/couldn't a white president say them?
Being of mixed race background, President Obama might have more credibility to take on matters of race relations in the US, where white presidents before him did not. He can also make a national apology for slavery and the crimes committed under that system that has sincerity and resonance behind it. Beyond that, I think Obama will need to be as presidential as any President no matter his race or gender, and this limits what he can and can't say in the public eye, for the public record.
I do believe that a black president is able to say things that a white president wouldn't be able to get away with. For some reason, it is very apparent in our society that people of a certain race can say a lot more abou their own race than people outside of that race can. I have had friends that are black, and being a white person, I have noticed that they are able to say more to each other than I or my other white friends would ever feel comfortable saying to them.
These issues I feel mostly surround the more touchy ones, like socioeconomics that follow certain groups of people. I think a black president will definitely be able to speak more to other black people about the issues surrounding the lower socioeconomic statuses of many black people (particularly in cities like Chicago). This gives Obama even more fuel to be heard, since he is not only black, but also from Chicago himself.
I also agree with sostrowki in that Barack Obama will be able to say things that a white president may not necessarily be able to say. For instance, Obama is less likely to be ostracized for speaking about touchy, race related issues than a white protestant male president would not normally be able to say. For instance, issues such as social programs have become racial hot topics and Barack Obama, being of mixed race will have an easier time speaking about such issues.
Conversely, I think that Barack Obama will not be able to make certain race related statements without looking like a "black nationalist." Though he has more a lot more leeway, Obama's skin color does not exclude him from being viewed in a negative light based on his words and views on controversial race related issues.