One great thing about several CSS3 properties is that they let you save bandwidth and write cleaner markup. All those extra meaningless div and span elements you used to be forced to add to create rounded corners? Not needed. The images used for the same rounded corners, for dropshadows, and for gradients? Not needed either.
Unless of course you want to achieve the same visual design in Internet Explorer. Until IE9 is out, IE users won't get any rounded corners, dropshadows or gradients created with CSS3. So it’s either living with that (which can be an option) or back to writing markup suffering from divitis and spanitis and letting your users download loads of images. Or you could try CSS3 PIE.