In the US it often depends on where you are. Larger cities tend to be more open and accepting. My wife breastfed both of our girls, often in public, with no problems whatsoever. Then again, we live in Los Angeles. I noticed fewer people brestfeeding in public in the South, but no problems in San Francisco/San Jose and New York.
A lot will depend on where exactly you are going. And the ignorance level of those you come into contact with. Being discreet, but not hiding, is my best advice and what always worked for us when traveling in different areas of the country.