I just got my ST-E3 and the 600EX and the only 2 sync options are first curtain and HSS - NO second curtain option.
Canon is charging outrageous prices for the new flashes and ST-E3 but did NOT update their ancient wireless ETTL-protocol to include flash on 2nd curtain. It is ridiculous and a real shame and one of the reasons I am holding off from buying an RT-set.
The Phottix Odin however enables 2nd curtain flash with Canon Speedlites, including 580EX/II and 430EX/II. It is obvioulsy neither difficult nor costly to include 2nd curtain flash in a radio trigger protocol. The Odin also allows triggering of monolights - even in mixed sets with Canon Speedlites.
I will wait to see, whether or not Canon brings out RT-receivers to include existing Speedlites (especially 580/II and 430/II) as well as monolights in a wireless setup and updates their wireless ETTL-protocol to include 2nd curtain flash.
These 2 features [2nd curtain, RF-triggers for existing speedlites and monolights] will be important factors in my decision on how to replace my 7D plus EF-S and EF glass in the future. The longer Canon drags its feet on this, the higher tNikon's chance to also bring out radio flash triggering with full iTTL support. :-)