But there is a problem with that. It will stretch the image to be 90%. I don't want an ugly, pixelated image at high resolutions. There has to be a limit to how low resolution the site should look good. Even w3c.org starts to breakdown at low resolutions.
Anyway, your suggestion would work in combination with a max-width property. Of course, IE does not support max-width, but after some quick research, there is an IE hack to do the trick:
http://www.svendtofte.com/code/max_width_in_ie/ Thanks, you got me thinking on the right track.