From an analysis of national exit polls by Faith in Public Life:
Obama beat McCain soundly among Catholics (55% - 44%), performing better than Kerry in 2004 and Gore in 2000.
Among white Catholics, Obama narrowed the Republican advantage from Bush’s 13-point advantage (56% - 43%), with McCain holding only a 5-points advantage (52% - 47%).
In a few key states, Obama made significant gains.
In FL, Catholics swung from the Republican party to the Democratic party. Obama improved upon Kerry's Catholic performance by 16 percentage points, from trailing by 15 points in 2004 (57% - 42%) to leading by 1 point (50% - 49%) in 2008.
In IN, a 13-point GOP advantage in 2004 (56%-43%) disappeared, with Catholics split evenly between the candidates (50%-50%).
However, in PA, McCain won Catholics 54%-46%, increasing GOP advantage from Bush’s margin of 52%-48%.