Making a semi-transparent background behind opaque text in CSS

When I receive the final PSDs from a designer I invariably want to reach through my computer and slap him for making my life difficult. With very few exceptions, there will almost always be at least one design element that is frustratingly hard to achieve using HTML and CSS (no matter how easy the designer may think it will be). The new properties available in CSS3 have reduced this frustration thankfully, but from time to time there are problems that crop up.