There was indeed an increase in evangelical turnout. They accounted for 23% of the electorate in 2004; 26% this time. That was supposed to fuel a McCain upset.
But Obama did, in the end, attract a meaningful number of evangelicals — more than wiping out the surge of Born Agains voting for McCain. Obama won 25%; Kerry won 21%
My rough count (since the results aren’t all in yet) is that Obama won two million more evangelicals than Kerry did. And McCain won about 1.5 million more than Bush did.
(See the ultimate comparative chart here)
UPDATE 2: It appears that Obama didn’t only gain among evangelicals in the rust belt. He also improved in some the west:.
Colorado evangelicals:
71%-27% in 2004
86%-13% in 2008
(I wonder how James Dobson feels that the percentage of evangelicals supporting the Democrat in his home state doubled since last election)
UPDATE: Mark Silk studies why Obama did so much better among evangelicals in Indiana but not in the South:

“In Indiana’s astonishing flip to blue, fully half the 21-point shift came from the evangelicals…. The most likely explanation for what happened in the South and Southern Crossroads is the persistence of racial prejudice in those regions. It’s also the case that this is where evangelicals are most heavily organized and mobilized as Republican partisans.
But in the Midwest, there is Obama’s identity as a Midwesterner, and the common Midwestern religious sensibility that he appealed to, to take into account. Not to belabor the point, but Obama’s communitarian outlook is very much the Midwestern way

.”