A new HTML5/CSS3 feature that will need some extensive exploration are elements with multiple background images. Here are a few links for further research into the many new possibilities this offers:
A warning for the kids: Now this is an example of what happens when you grow up with too many 8-Bit games hammering your poor brain.
What was the first thing - literally the very first thing - that I could think of as a possible use of multiple background images: Parallax Scrolling!
As it turns out, these new CSS features open a third avenue to rendering animations besides SVG and Canvas. And for certain animations, it is actually a very attractive way to code this, since all that has to be changed per animation cycle is only one line of CSS: the position of all the composited PNGs.
No Flash, no Canvas, no SVG - just a DIV:
Sorry, but we have to trick the spambots... How much is 2+1? *: