What Lanny says above sounds useful. I also like Douglas Bowmans suggestions for the gradient properties. (Yes, we want gradients!!)
I also really REALLY like the sound of HSL colours and semitransparent colours using RGBA/HSLA. Sweet! (Looking forward to being a CSS3 designer, you bet.)
Another thing from the above comments that sounds useful is the suggestion for {background-repeat: down | up | left | right} and not just x vs y.
As others have said already, please let us set border-radius on a per-corner basis!
Carsten Altena’s suggestions above for rotating and flipping a background image sound great. Could be useful.
Faruk Ates suggested {gradient-interval:[length]}. If you’ve got the time that would be great to have, too. 🙂
Thanks for reading!
ps. Feels great to be able to give direct feedback like this.