Okay, if you haven't read this amazing article on alistapart I think you should head over there now and read it.
Eric Meyer (of so much CSS fame, if you don't know who he is you're here for the wrong reasons! Or if you would like to learn head overt to Complex Spiral and be amazed!) delivers a beautifully written, and very comprehendable argument for the use of vendor prefixes in CSS3.
The article basically states that the vendor prefix (e.g. -moz, -webkit) is a great way to allow vendors to test, or beta the newest technologies they support. It allows for progressive enhancement in a non-detrimental way to your website. Adding or removing a couple of lines to add extra functionality (or remove them once fully supported) is a lot cleaner and easier than those umpteen nasty hacks we used to use to clean up pages for IE <= 6.
Do you use vendor prefixes for the latest CSS3 techniques? Let us know below.