I have written a RPG called "Chuť magie" - it's in Czech and it means literary "Taste of Magic", but I'd definitely call it "High on Magic" in English. I'm not planning to translate it to English soon, unless paid for it significantly, but I'm curious how original is it :-)
It's based on simple presumptions: 1. PCs are magi 2. magic is highly addictive and leads to temporary (or permanent) insanity
There are other alternative and quite original features (no GM for example), but I'm asking about originality of the magic system, where magic is limited by making the mage PC do weird or funny things, which have in-game consequences (they are not just flavour)? The PC can be forced to do such things either directly ("you must...") or indirectly ("you are penalized, but you can do XY to erase the penalty" - this is what I use there). Do you know about such a system (or subsystem for magic within more general game)? Or, ideally, list of such systems as complete as possible?
EDIT to clarify things: Mage can do almost anything, limited by complexity of the spell, his magical abilities and level of "tipsiness", the measure how he's "high" on magic. The more complex the spell, the lower the chance of casting and the more tipsiness the mage gets. Tipsiness work as a universal penalty, but it can be decreased by doing non-magical hobbies (important trait of a PC - these can be normal or strange, but should make conflicts with other characters, because the system encourage it) or playing symptoms of magical intoxication, like casting spells the mage has almost no chance to cast succesfully or do other (almost) impossible things, insult others, break things etc. Any player can trigger this, but the PC's player can increase his tipsiness and get a saving roll. These strange things usually have some consequences, they are not just consmetic effect. This is where my original formulation was bad - it didn't exclude "just flavour" effects, which are nice, but not exactly what I wanted.