Still haven't gotten a Beta key, but I've hoped onto the PTR to check out the changes coming with patch 4.0.1. I have to say the new UI features are great. The spellbook layout is very useful, being able to see what spell is available and when is an excellent change. The additional tabs for professions and pets in the spell book are handy. I really like how you see the names of each pet and mount.
More to come later.