Technically, browsers are supposed to drop the prefixes when the spec reaches Candidate Recommendation.
The moment before your code looks like this, you use Sass.
Re:The Shapes of CSS
by chriscoyier on Saturday August 13, 2011 @12:25AM
(#2880242)
I think it's nice to see. It means the spec is probably pretty close to being finalized, because in order for that to happen, there needs to be at least two browser implementations.
I know that technically, the transform specs are not finalized, but considering this kind of consensus (even IE seems to agree), would it even be wise to change the spec again?