Craig Buckler has written an article about abolishing CSS vendor prefixes. You know the prefixes, you need to test early implementations of CSS properties. The issue is that people have these properties harcoded in their style and they are unlikely to maintain them on the longterm (forgetting, doing something, no money from the client, etc.) Even if experimental, the property being more or less well implemented across browsers, people use them intensively. Too tempting :)
Are vendor prefixes still required in an age of increased browser co-operation? I doubt any developer wants to use prefixes but are they a necessary evil? Would it be better if vendors added properties without prefixes, but made it clear they were experimental and not (yet) a standard?
If I had the choice, I would go an intermediate radical way (Yes It is strange). I would make the vendor prefixes usable only in the Developer mode of the browser. Most browsers have now a Developer mode. Once the developer mode is activated, the CSS vendor prefixes are shown, but for the vast majority of people, this never happens. Then the vendor prefixes are not usable for production with wide audiences. Web developers in Web agencies will not use them for business only for pleasure.