I did an update - using factory - from rc1 (kde 64 bit) and was amazed to see that there were over 1,100 updates. Pretty impressive since rc1 only came out so recently.
New kernel, some updates to xorg and slightly newer kde 4 packages are what caught my eye.
Two practical changes (for me) that I noticed - no error screen message when installing the nvidia driver (from the nvidia d/l) and aaa_base no longer causes a kde crash notification message after closing a kde3 programme within kde4.