Isn't CSS3 supposed to have an opacity setting (little use considering not every browser supports it now, but, might be something to look forward to?)
EDIT: Correction, not "have", rather "support"
EDIT: Correction, not "have", rather "support"
On some sites, I've used it as a subtle hover state for image links, so they "pop" a little. (Set the default opacity to 92% and have it go to 100% on hover.)