Chrome/Webkit will start to support the OpenType features version 18 from what I have seen - no idea about Safari yet. The current Canary build has support built into it but at this time it is only for Windows and not on the Mac. Not sure about the issues around the Mac and why they might not support it out of the gate but I assume they are working on it.
They will use the -webkit- prefix for the font-feature-settings. So like most new things we will have -webkit -ms and -moz until it settles down.