Low downs:
(1) The law: you have to have a working visa in order to be able to work. You can get it through the German consulate before travelling or through the "Auslaenderbehoerde" where you'd live. An American has fairly good chances of getting one if they convinced the German government that they can do something that ordinary Germans don't (most of the people I know got their first working visas as ESL teachers). If you enroll to a German university (tuition is very minimal in Germany), you can work for 40 hours a month.
(2) Economy: In many places in Germany, and especially in hip places like Berlin there is sharp unemployment now. Baden Wurtmberg has less unemployment, but "foreigners" always suffer. However, I am in the believe that if you have the will, you'll find something.
(3) Societal reactions: I am not black. However, there is racism in Germany. Don't think otherwise and be prepared to deal with it. Racism doesn't always mean violence - usually it is much more subtle: you might have harder time getting a job than a "white" American, you might find some people treating you suspiciously, like an illegal immigrant from Africa, and getting relaxed only when they hear that you're American, etc.
I think basically that German society has a very good quality of life and is very relaxed, but as an immigrant, you'll have some time to adjust and be prepared that the beginning will be rough.