I'm not terribly well-informed politically, so my general approach to politics is to find someone who is well-informed and vote for who they vote for. In a sense I'm exercising my own tiny version of proxy voting. I'm pretty circumspect about who I'm willing to consider acting as my proxy. They have to be intelligent, thoughtful, and morally compatible with my beliefs. More than any other politician I've seen in a long time, Obama strikes me as the kind of person I'd be willing to trust my proxy vote to, which is really what you want in electing any representative, particularly a president.
By the way, you can also see this speech on YouTube. It's long, and definitely not as polished as the DNC speech from 2004. But perhaps if you want to see what a less-thoroughly-rehearsed Obama speech looks like it might be a good one to check out.
[Edit: props to cabanasloth for posting the original speech to LJ]