First, this is a normal guy.
I've spent time with a lot of politicians in the last 15 years. Most of them talk at you. Listening is not their strong suit -- in fact, many of them aren't even very good at faking it. [ExTP anyone???]
Senator Obama, in contrast, comes across as a normal human being, with a normal interaction style, and a normal level of interest in the people he's with and the world around him.
We were able to have an actual, honest-to-God conversation, back and forth, on a number of topics. In particular, the Senator was personally interested in the rise of social networking, Facebook, Youtube, and user-generated content, and casually but persistently grilled us on what we thought the next generation of social media would be and how social networking might affect politics -- with no staff present, no prepared materials, no notes. He already knew a fair amount about the topic but was very curious to actually learn more. We also talked about a pretty wide range of other issues, including Silicon Valley and various political topics.
With most politicians, their curiosity ends once they find out how much money you can raise for them. Not so with Senator Obama -- this is a normal guy.