Have been accumulating the system as I can afford it, I now have the ST-E3 controller and four flashes. A couple of comments after the review:
-The price of the flash has actually been slowly falling. The last two I paid $529 from Adorama in person.
-One thing I'm unhappy with is that if you're shooting in low light you really need a 600 as a controller if you want the IR focus assist. Of course you can turn off the flash on the shoe if you're using it as a controller with other flashes off camera.
-It's easy to mix with studio strobes. If you use the ST-E3 to trigger a 600EX being used as a hairlight or something, the 600EX will then optically trigger a studio strobe in a softbox or whatever. I use it together with my older Elinchroms like that.
-As far as the filter issues, I use a Honl speed strap along with their filters. I'm sure there are other workarounds as well.
-It definitely took time with the manual to figure it all put, plus looking at Neil's Tangent site, and some of the videos at canonlearning, but I'm quite comfortable with the system now and love it.
-I wounder why a controller can control just about anything on a slave, but not the zoom range. That would have been cool.
Overall am very happy with the 600EX-RT system.