Should have added this earlier: remember that the ST-E2 can only do two channels of remote flashes. I've never used one, but from what I can see it cannot trigger flashes by power level, only by A:B power level ratio +/- any flash exposure correction. As such, you won't be able to fully subscribe to the strobist method by setting manual power levels at the camera or on the flashes. I often use three channels (key, fill, background), sometimes use preset power levels instead of ETTL, and occasionally wish I had another channel or a means to trigger additional flashes (so I could dial in a preset power).


As far as shoot-through umbrellas, they do run the risk of spilling light where you don't want it, but you can get more power out of them by shortening your effective lightsource-subject distance. I've started putting up a gobo to keep excess light away - it works for me.