He or she doesn't have to slice for HTML or CSS3 though if they want to and can then thats good - but the important thing is that they can make a beautiful layout.
To give you an idea, I am thinking along the lines of rounded corners and shading.
I probably don't want the elements in .png files, and would prefer in CSS3 - with the best compatibility possible with IE but accepting the limitations.
Do you know anyone who designs lovely stuff like that?
If so, send me details.