If you’re going to use CSS3 properties in your designs, it’s a good idea to make sure you aren’t trying to apply them where they aren’t supported. Old browsers have a hard enough time trying to grok your newfangled HTML(5). Don’t confuse them with transforms and text shadow.

You can use nested CSS selectors in Compass or SASS syntax to make browser feature targeting with Modernizr.js really easy.

Modernizr creates an html class if the feature is available in the browser rendering the page. Just wrap your styles with the selector for the feature you’re using like so:

Nested Modernizr Classes with Compass
modernizr_nested.scss
.textshadow {
    .widget h3 {
        text-shadow: -1px -1px 0 #aaa, 2px 2px 5px #3a3a3a;
    }
}

If you really want to go the extra mile for performance, use Modernizr’s built in YepNope.js conditional loader to load feature specific stylesheets or Javascript only when they can be used.