Went to Belgrade and Sarajevo last year and cant say there was any difference in safety to the rest of Europe. Bosnia and Serbia are safe and fairly modern countries. Never been to Albania, it is a bit more run down and does not seam to have a good image, but there’s no great safety issue’s i have heard of.

Bosnia and Albania are fine, despite a few landmines in out of the way places. When I went to Serbia I didn’t feel as if people were too happy to meet me because I was american, and that was before Kosovo’s independence and burning the US embassy. But I suppose tensions ease over time, just not sure how much time it takes. I doubt you will encounter any hostility, but if you are american, don’t be surprised if some people don’t act friendly.