Multiple background images are part of the CSS3 Backgrounds and Borders 
Module [1], and currently supported by Safari [2].

Sincerly,

ACJ

[1] http://www.w3.org/TR/2005/WD-css3-background-20050216/ 
[2] http://webkit.opendarwin.org/blog/?p=15 

Lonnie Best wrote:

> With the "background-position" style property, we can position a 
> *limit of one* background-image so that it "docks" against
>
> any "side or corner" of a block element.
>
>  
>
> I propose the ability to "add and position" *multiple* background 
> images for a "single element". With this specification, a
>
> designer would be able to "round the corners" of any element without 
> having to make style rules for any other element!
>
>  
>
> [...]