Eric Meyer, in praise of browser prefixes such as -webkit:

If the history of web standards has shown us anything, it’s that hacks will be necessary. By front-loading the hacks using vendor prefixes and enshrining them in the standards process, we can actually fix some of the potential problems with the process and possibly accelerate CSS development.

I’d add that vendor prefixes work very well with a steady diet of progressive enhancement. You, as a developer, are not bound by law to make every element on every page look exactly the same in every browser. The less tied-down each of us are, the faster all of us can move.