I think the last few years have greatly changed traveling to countries in the Middle East. Unfortunately the hard liners have taken over. I'm guessing the majority of people would be welcoming to Americans, but they are no longer in charge. We sat on a plane from Barcelona to Munich a couple of years ago next to a very friendly, engaging Muslim from Cairo. Awesome guy but even he said Cairo was getting very dangerous for everyone and he didn't recommend anyone traveling there.
On the opposite side, in the last 4 years I've been to Sweden, Finland, Russia, Denmark, Norway, Latvia, Estonia, Germany, France, Austria, Switzerland, Spain, and Italy. Those people were awesome and we often walked in small towns by ourself. Never once felt threatened and people were extremely welcoming to Americans. I'm 6'4" so I stand out but we always wore plain clothes not to give away our identity. People still started speaking English to us when they saw us-- they just knew by our dress, hair, etc. The last day in Germany I just gave up and wore a St. Louis Cardinal t-shirt. I noticed no difference in behavior toward me then either.