CSS3-Borders:
Without using Photoshop or other design programs you can use images as borders, add shadow to boxes, and create rounded borders. For example, when creating rounded borders, it’s as simple as adding in your “border-radius” property.
CSS3-Fonts: Before CSS3 was made, designers had to use fonts that were already installed on the user's computer. This is not the case anymore, designers can now use whatever fonts he/she wants to use. Whenever the designer buys/finds the font they want. All they have to do is include the font file on the web server, and it will automatically download to the user when needed. How cool is that for a change!
CSS3-Animations: Animation is a new CSS property that allows for animation of most HTML elements without JavaScript or Flash. At the moment, it’s supported in Webkit browsers, including Safari 4+, Safari for iOS (iOS 2+), Chrome 1+ and, more recently, Firefox 5.
Unsupported browsers will simply ignore your animation code, so make sure that your page doesn’t rely on it! Because the technology is still relatively new, prefixes for the browser vendors are required. So far, the syntax is exactly the same for each browser, with only a prefix change required.
That is just the icing on the cake as many would say, but for a more in-depth look I really recommend looking at the W3schools link toward the top of the page.