I don't know about technical censorship, but they certainly massage the algorithm to get the results they want. Google 'American Inventors' or 'how to commit suicide' for a quick demo.
The American inventors thing could easily be a result of the population of websites that Google is sampling from. Culturally, "African-American Inventors" is a much more common topic than "America is so great, look at all of the inventors that live here." So if you randomly and fairly sample from every web page, you are likely to end up with exactly what you end up with.
(Disclaimer: I have not actually checked to see what the baseline distribution of websites is, I'm just guessing.)
(Disclaimer: I have not actually checked to see what the baseline distribution of websites is, I'm just guessing.)