Nate Silver at 538 notes this disparity in donation amounts:

More than half of Mr. Obama’s fund-raising total has arrived in donations of less than $200. Just 13 percent of Mr. Romney’s fund-raising has come in such small denominations. Instead, a majority of the money Mr. Romney has raised arrived $2,500 at a time, the maximum campaign donation allowed for either the primary or the general election…

For the Romney campaign, however, a paucity of small-dollar donations is inauspicious not because it means that it will have trouble raising enough money (it probably won’t, and if it does, Mr. Romney has considerable personal wealth at his disposal). Rather, a lack of small-dollar donors could indicate tepid support for Mr. Romney among the Republican base.