Internet Explorer has a number of interesting capabilities that can improve your web page look and feel with costing your web site lots of bandwidth usage.
One of these techniques is to use VML to render gradient backgrounds on your pages. While VML is currently only supported in IE 5.X or greater, it would be possible to determine which web browser a user is using, and output either VML or a background image for the background.
Users with slow dialup connections wouldn't have to wait for a gradient background image to be sent to them. Only a few extra bytes of code in your HTML file are needed to do the same thing!