This is a big one.
According to Fox News, Pennsylvania has been called for Obama. The McCain camp had been leaning on Pennsylvania and hoping for those 21 electoral votes. In Pennsylvania, 81 percent of Hillary Clinton Democrats voted for Obama. Also according to an exit poll, Obama’s remark that “John McCain is out of touch” was agreed with by 64% of voters in Pennsylvania.
This one is definitely a big pickup for Obama and certainly hurts McCain’s chances in the big picture. But it is relatively early and there still are some possibilities (not many) for McCain.