From the Washington Post, “Big donors drive Obama’s money edge“:

Lost in the attention given to Obama’s Internet surge is that only a quarter of the $600 million he has raised has come from donors who made contributions of $200 or less, according to a review of his FEC reports. That is actually slightly less, as a percentage, than President Bush raised in small donations during his 2004 race, although Obama has pulled from a far larger number of donors.

Mark my words: this will cause problems for President Obama.