The answer will likely vary from country to country, and I'm primarily interested in Canada.
I do a version of 'street photography'
http://frankgross.com/portfolio/portfolios/untold-stories/and the people in the images are for the most part recognisable.
I do not approach them for model releases for a variety of reasons.
The images are never sold as stock photography or for other 'commercial' purposes where the image is used for commercial gain.
However I was asked to show the images at a city wide 'art festival' in Montreal where they'd be printed large and displayed publicly.
The curator is concerned about being sued if someone recognises themselves.
The same question would apply if I exhibited the images in a commercial photography gallery or even a 'coffee shop' or sold prints from my website.
My thinking has been that millions of images are taken in this way (think magnum agency and a myriad of other photographers), and the images are often sold in galleries, published in books, used for editorial, without recompense for the subjects therein.
I came across the attached pdf which pertains to Ontario but I'm not convinced it's legally watertight, or even who the author is.
Does anyone have experience &/or knowledge to share?