If you'd like to experiment with the new CSS3 properties, you'll have to be sure to prepend your properties with vendor-specific prefixes. While these properties are supported by most modern browsers, they are still under development and may be implemented in slightly different ways in different browsers. Take for example, this bit of CSS, which rounds the bottom two corners:

.sf-menu ul li:last-child a {
-webkit-border-bottom-right-radius: 7px;
-webkit-border-bottom-left-radius: 7px;
-moz-border-radius-bottomright: 7px;
-moz-border-radius-bottomleft: 7px;
border-bottom-right-radius: 7px;
border-bottom-left-radius: 7px;
}

You can see that the property for the bottom-left and bottom-right corners is slightly different between webkit-based browsers (Safari and Chrome, mainly) and Mozilla browsers (mainly Firefox). After the vendor-specific code, include the general CSS3 code for any browsers that support that to make sure your code is future-proof.