I wouldn't argue that this is a perfect metric of netroots support, but it's not bad either. What we've got here is a huge disparity between Barack Obama (28% of his $58.9 million in contributions were $200 or less) and John Edwards (24% of his $23.1 million) at one extreme; versus people like Chris Dodd (1% of his $12.1 million), Joe Biden (4% of his $6.5 million) and Hillary Clinton (7% of her $$63.1 million) at the other end of the scale. I don't believe that "following the money" tells you EVERYTHING, but it does tell you a great deal.
P.S. For more, see the New York Times.