OK, so Westeros is a little fatter on the west coast, and there's clearly a Dornish peninsula that was added later. But on the whole, it's pretty close to identical. As George told us, the Fingers in the northeast match perfectly with the Dingle Peninsula, King's Landing stands in place of Galway, Donegal Bay is replaced by the Sea of Dorne, while Belfast and Dublin mark the positions of Oldtown and Casterly Rock respectively.
But that only accounts for everything south of the Neck (where that massive dickbag Walder Frey lived, until recently). So what about the north of Westeros?