One of my friends was so discreet most people would not have known she was breastfeeding - she always tried to find a quiet, private place for her benefit - she is a quiet and reserved person - but when that was not possible she always managed to feed her son discreetly - she obviously gave careful thought to her clothing - she also had a small shawl that fitted over her shoulder.
Recently I was sitting at an airport and a young woman sitting in the departure lounge breastfed her baby on and off - she was wearing a tube top and just pulled it down when she was feeding so she was naked from the neck down to the waist - with one breast totally exposed the whole time. I thought this was a bit much although I'm sure the men sitting around me thought it was a fine show. It's only the extreme examples that I notice - otherwise I'm busy doing my own thing...

I feel fine with women nursing in public, but I do think it is important to try to be discreet. It's really easy to nurse without exposing one's whole breast. I do know one of those "over the top" nursing Moms, and people who don't blink about nursing in general are always chattering about her.