Jon Austin (08.03.12, 7:18 PM): I just upgraded from 3 580EX II's and a 420EX to 4 600EX-RT's. I don't shoot wireless very often, but I do have one important, regular portrait gig every year, which requires shooting 2 Speedlites into umbrellas, with a 3rd used as either a hair light, or to illuminate a backdrop. Getting the optical Speedlites to "see" the master was always problematic. Really looking forward to my first wireless shoot with these! I also like the new menu system; it seems much easier to navigate and configure controls as desired, without constantly refering to the manual. I would have purchased an ST-E3 in place of one of the 600's, but was put off by its lack of AF assist. Boz (05.20.12, 4:46 PM): Bit the bullet - sending 580 in for repair, $180 repair bill :( Cheaper than replacing though, and I believe it's a simple thyristor problem, otherwise still in excellent condition. Boz (05.19.12, 8:15 AM): VERY Helpful info Michael - My 580 is not firing like it should be, going to have to send it in - afraid of how much that is going to cost. On the other hand - gotta me so much cheaper than the 600, even if I have to replace it with another 580.