One thing I did with horizontal white gradients was to have a white background. Using CSS to control the z-order, had the gradients at both the top and bottom of the page. Using DHTML to provide an alternate method of scrolling up/down the page, the end effect was images/text between the two gradients would look like they faded into the white background as you scrolled up or down. The page contents were just under the gradients, and as the text/images slid under the transparent portion of the gradients, becoming more opaque, the effect was like watching something slip into mist. I'm sure with some time someone could put some Bryce clouds and make it look more realistic.