Wild mushrooms are harder to identify. Other than the few I can readily identify on sight, I use an identification guide. There have been several cases of people (almost always from the Far East) inadvertently dying after eating death caps (Amanita phalloides) which I've read taste delicious but are fatal, and can take days to kill:
http://www.iwcp.co.uk/news/second-mushroom-victim-critical-i...
http://www.abc.net.au/news/2012-01-04/two-die-from-death-cap...
http://www.abc.net.au/news/2012-06-08/woman-dies-after-eatin...
They mistake them for paddy straw mushrooms (Volvariella volvacea) which look identical and are used in Chinese and Thai cuisine. They can be distinguished by spore colour but a better way is to check it came out of a tin before eating them.