So as of today, a black man is president-elect of the USA. Even if he completely fails to live up to expectations (although I really hope he doesn't, for all our sakes), nothing will change the fact that there are black people in America who remember being 2nd class citizens and not having the right to vote, and now one of their own is going to run the country, in their lifetime. From my position of privilege, I'm finding it hard to comprehend how huge that must be for them. (ETA: which is not to say it isn't a big thing for all of us and that we don't all benefit from increased equality)
The thought of having Sarah Palin as Vice President when McCain is eldery and not exactly hale and hearty, was always much scarier to me than the thought of McCain as president (I might not agree with his policies or the way he conducted his campaign, but i think he is at heart a person worthy of respect and not an utter nutcase like she is), but now there's a liberal intellectual heading into the White House, and from my place of liberal intellectual bias, that's a very good thing for world :)
ETA:
This blog post is the most eloquent I have found on why this is so important. Read it and weep for the right reasons.