I've personally witnessed it (not my own cat!) with a friend's roommates' cat. Trust me, I almost went and took the cat away myself to the shelter I volunteered at, but he sent it to live with his parents thank g! If you run into any bright people who think its a good idea, you'll encounter all kinds of idiotic ideas: blowing it in their ears being one of the most ridiculous.
This cat ate up to an ounce once and also people would "hotbox" it if you know what that means. This cat was fairly regularly blazed and began to show signs of addiction, like if someone in the room had any (I don't smoke it either) he'd be scratching at their pockets trying to get at it.
Last I heard, this cat is huge, drools consistently (like a St Bernard), and can't see very well and who knows what else. I doubt he'd ever have taken it to the vet. It was one of those, oooh look at my new kitten, I bring it everywhere, it sleeps on my chest, and suddenly three months later he was sick of it sort of deals with people who should never be allowed to have pets.
From what I saw, I would never let a cat near the stuff. I have heard that its permanent as well and it may very well be, the way acid is permanent in humans. I'm sure it lasts for weeks, and since THC is fat-soluble and cats don't metabolize fat the way we do I find it totally plausible. Write the Straight Dope!
And, a good explanation from Marvista Vet:http://www.marvistavet.com/html/body..._toxicity.html