Serbia

Traveled to Belgrade and Subotica when traveling between Bosnia and Hungary about 5-6 years ago and didn't have any issues. Didn't notice any difference in treatment one way or the other.

One of my coworkers is married to a Serbian and travels there once a year. She's never mentioned any anti-American feeling. I think Serbians are pretty easy going. Even as somewhat of a Russian satellite, expect to be treated the same as any other visitor.

I am not American but I was in Serbia (Belgrade) in May and I am not sure why it sometimes gets a bad rep.
I thought the people were nice and helpful in general. None of the serbians that I met had bad things to say on Americans even when I mentioned that I am not from there (but live there). Very compact city (easy to walk to many sights) and cheap food&drinks. Nothing to worry about I think.

I visited Belgrade for two nights in May 2015. I never felt unsafe and people were friendly. I read online that it would be best to avoid discussing politics, and that's good advice when interacting with strangers in any country. That being said, the manager of the hostel did rant briefly about Kosovo while discussing the history of Serbia. He wanted me to know that reports of Serbian atrocities were exaggerated and ethnic Albanians did horrible things to Serbs. I was not about to get into it with the guy and politely changed the subject. This was only one person, but I definitely picked up on a strong nationalistic vibe when talking to others. I suggest expressing interest in the Serbian culture and not broadcasting the fact that you're American. The U.S. led NATO air strikes and you probably don't want to spend your vacation engaged in awkward conversations. Also, per the U.S. State Department, travelers should avoid the Kosovo border region. I suggest checking the State department travel advisory website while traveling outside of Western Europe.

I suggest read up on modern Serbian history, good , bad, and the ugly. Knowing that will help you detect this nationalism. When you check in at the hotel or hostel, they'll know you are American. I'm interested in going to Belgrade too and Novi Sad, reachable from Belgrade.

Fred, I will be there in about 6 weeks. Will let you know if I get thrown off the roof. Naaaa, I have some Serbian friends and from our conversations I feel very confident.