I've done two days of it now and WOW is my core feeling it! My upper and side abs (can't think of the actual names) are really sore. My low back too. But in a good way. And surprisingly so are my legs (especially my inner thighs, nice!) and glutes.
So far I like it more than the 30DS. But I think it's because Jillian is a little less annoying in this one. A little.
Has anyone else done or doing it right now?