Yes, it was a big deal when I was in school in the 70s. Everyone played. There were never any conkers left unclaimed under any Horse Chestnut within a mile of the school. We all tried lots of tricks - soaking in vinegar, baking in the oven - practically anything was allowed, but I'm not sure any of it made a difference. It could be pretty painful as getting your hand hit by a high speed conker was common occurrence, but I don't recall anyone getting any lasting injuries.