All the Himmies I have known were very friendly - when I was in high school, I babysat for a family that raised and bred them as show cats. It was very hard to do homeowrk with a Himmy plunked down on your Chemistry textbook, I can assure you.

They can be prone to some problems that any "push-faced" critter - dog or cat - gets. Some of them snore (very quietly, they ARE cats, after all). Some of them get tears a lot, and so you just need to keep their faces clean. And, of course, brushing is pretty much manditory, but that's true with any long-haired cat.