It isn't too intensive afaik. That was the whole point Jobs made about Core Animation - that it was able to simplify this, and be able to do real time demos of what was previously only doable via a huge amount of intensive computer time.
It's something that hasn't been really talked about, but there is a bit of a void Core Animation wise - we havent' seen too much action on it - hopefully come the SDK release, we'll be seeing it in a lot more applications (like recent recoding of Quicken the Accounting software) and more snazzy stuff for viewing videos/pictures/interactive and not just passive like the picture screensaver/the album art building builder