Not being British, I missed out on some "great ideas" like this: the Lenslok.
The two most irritating copy-protection schemes I encountered back in the old days (both from Sierra games)had different flaws. One had the flaw of completely interrupting your game. As I recall it, in QFG4, there was a puzzle that required you to reply to randomly coded questions. The codes were stored on the game disks, and given computer limitations at the time, required me to write down the question, quit the game, load up the code info, look up the answer, write that down, and then start up the game again in order to enter it. More than once. Urgh. (My memory may be failing slightly, but that's how I remember it - the file was on the CD because they couldn't bother printing a manual. Admittedly, this meant you couldn't LOSE it, see below)
The other was a good idea poorly executed. It was a mystery game and the copy protection required identifying a fingerprint, which you could look at on a codesheet with a special red-filter magnifying glass. Unfortunately, both the sheet and the 'magnifying glass' were as flimy as possible, and very soon LOST, making the game rather problematic to play. If they'd made decent feelies out of the copy protection it would have worked a lot better IMO.