Upgraded my 580EX II to a 600EX-RT a little more than a week ago. I just want to warn you about one nasty aspect of the otherwise marvelous flash (pictures look way better with this one than with the 580EX).
Most of the time I’m using fill flash for bird photography. You know, Better Beamer and high speed sync (HSS). The latter is the problem point. The flash already was in my hands when I read that it DOES NOT support high speed sync with older camera models. Bummer. This omission should be advertised with huge burning letters IMHO…
The results: I’ve used the 600EX/1DII combo on three occasions. On the first, HSS sometimes worked, but turned off from time to time. So I had to keep an eye on the flashgun’s LCD to check whether it’s still active. It always went away when then flash entered sleep mode – which I turned off completely. During the second shoot I was unable to make it working. The 3rd shoot however went without a problem.
Did I say that I really like the “fully charged” beeper?