I work in memory research, and went to a conference this week in which Bob Logie at Edinburgh talked about an on-line set of memory tasks they've developed. They're on the BBC, try and them, they are pretty good actually. Most of them are based on proper research rather than being daft stuff knocked up by idiots. http://www.bbc.co.uk/science/humanbody/mind/surveys/memory/
the pound coin one was hard so many things you use every day but never notice what they look like exactly.
I know I got that one wrong too. Strange isn't it, the things you process and the things you ignore. Its fascinating how memory for some information can be so detailed and robust, yet for other stuff we struggle to retain more than a few bits of information.