Paul Waldman puts Romney's small donor problem in context:

[M]oney raised by the Romney super PACs will be less influential than money raised by the campaigns. He will no doubt be able to find plenty of big donors who will give his super PAC a million bucks or so each. When a donor does that, the million bucks gets spent on TV ads and mailers, which is all well and good. But it doesn't support volunteers (no one is volunteering for a super PAC) who make phone calls and knock on doors, and multiple studies by political scientists in recent years have demonstrated that personal contact is far more persuasive than things like TV ads.