.css('background-image') returns:

url(host/folder/file) in ff3.1

and

url("host/folder/file") in IE (note: the quotation marks!)

not testet in other browsers.

this code worked for me as a temporary fix:

function getBackgroundImageUrl(el) {

var url = $(el).css('background-image').split('(')[1].split(')')[0];

var url = $.browser.msie ? url.split('"')[1].split('"')[0] : url;

return url;

}