Grassroots, as I understand it, is when the movement is not orchestrated, but just springs up around the politician. Ron Paul and Huckabee certainly qualify, but I don't see how Obama does.
Okay, Obama isn't grassroots. But he has still put together the single most powerful team of volunteers any election has seen. And he's orchestrated a lot of it over the Internet.
Government is a compromise between the benefits of collective action and the drawbacks of other people influencing those actions. We're not in the right place on the spectrum.
I support Obama because he has a reasonable approach to foreign policy, he cares about open government, he's ridiculously intelligent, his party isn't theocratic, and Sarah Palin isn't his running mate. I could do without the anti-trade sentiment, continuing the coupling of healthcare to employment, etc, but you work with the hand you've been dealt.