I'm often shocked to find out that some actors really aren't American (and vice versa). I guess that's the idea of acting to begin with. There are lots of talented actors on both sides of the puddle that do incredibly well.
I just watched Across The Universe and had no idea Bono was in it until he started singing (I thought it was Lemmy from Motörhead at first!

) -- and
his American accent was spot-on!
I'm from NJ, though, and worked in NYC -- yet even The Sopranos accents are a bit much for me!

PS:
ö works, but ö doesn't