This is an article about a book that I've been meaning to read, which directly mentions Othello's probable inspiration. Keep in mind that, for Othello to have resonance, both his position of power and the racism would have had to resonate with Elizabethan audiences:

http://www.telegraph.co.uk/books/what-to-read/why-elizabethan-england-was-obsessed-with-islam/

As far as I understand, it was uncommon- but less so than we imagine. The 'East' (incorporating North Africa) was still the centre of world trade, and there are numerous accounts of individuals travelling across continents, working in trade, diplomacy, and religion. Certain communities were less welcoming (consider the expulsion of the Moors by Catalan/Spain), but there certainly were many (and increasing) interconnections, and experts in their field were valued.