i was over in amsterdam in feb. was great, i'd defo recommend going to the zoo and hit a coffee shop before you go there! just hop on a tram (maybe number 3) and it stops right outside.
in the little shops on some streets there were selling mushrooms, they weren't on show but the person behind the till would start talking to you and if you seemed interested in that sort of thing he would offer some. dont know how common this is though. the bulldog coffee shops was the best we went to i think. hope this helps