Re: Travel to Europe...
The cities I'd recommend would be: Berlin, Zurich, Bilbao (had friends there, though), and Cinque Terre.
I agree with SunDeck's advice as well. Less is more when traveling Europe. I'd much rather get an intimate feel for a couple of cities than a rushed glimpse of a dozen.
And as for sticking out as an American, I had little to no problem. But just like over here, there's a certain number of jerks in every crowd.