I don't know whether this is a font/configuration issue or a bug. If I look at a certain web site, the degree symbol is displayed as a black diamond with a white "?" inside it in Safari 6. It displays properly on the same Mac using Chrome. It displays properly on an iPhone and iPad using iOS5.1. So I suspect this is a Safari 6 issue.
This is not a major problem, just an annoyance. If anyone has an idea for resolution, I'd sure appreciate it.