I have never ever played her either, haha. It's something about support champs that doesn't seem too interesting. The only support champ I've probably only ever played was Soraka and she wasn't too bad.
Maybe it's because all you play are AD carrys. /EDIT: Specifically Vayne. /EDITEDIT: Also, Karma sucks monkeytits. Her heal is far too conditional to be a good support, and her damage is too low to be a carry.
I have just about every champ but I've only played like half of them. I normally find one I like, main it for a few weeks and then go back to other old champs I liked, only once in a while do I add a new champ to that list.