Are candidates allowed to walk around handing people money?

Romney hands some poor woman $50 as a campaign stunt. There's no law aganst campaign stunts, per se, but in general terms handing out money is frowned on, isn't it?

Hypothetical: A candidate says that the first twenty unemployed voters at each campaign event get a crisp Grant. (Or is a $50 bill a Ullysses?)

Is that legal?

Not to be too petty, but didn't it used to be against the law for candidates to hand cash to potential voters in a political context? I seem to recall some scandals about "walking around money".