I always do normal content blind. This content is easy enough to figure out if you're paying attention and your brain is not turned off. It's also not very punishing. And I agree that figuring out stuff on the fly is really fun, though I can see how a healer might find this stressful (I play DPS).

As for high-end content (Savage, Extremes, etc.), I can only go in it blind with the right group of people. Everyone needs to be on the same page when it comes to blind runs. I don't want to be a burden to anyone, so I don't feel comfortable doing high-end content blind with strangers.