Summary: First of all, I think this is a very nice flash, same as my 580EX and 430EX. The recharing time now is even faster than the original 580EX and the build of the flash is very sturdy and I think it's going to last a long time.
Pros: 1. Faster recharing 2. Weather-sealed 3. Overall built
Cons: 1. The master/slave switch is now gone; very inconvenient 2. New design on the hot shoe and connecter. Will not work well on bodies prior 1DIII
Summary: I bought this unit after playing with one that belongs to my friend. If you are not a hardcore enthusiast, there is a tough decision between this and 430EX. Both are very good for their respective prices.
Pros: more range, master mode, works with external power source
Summary: One of the first things I noticed and somewhat anticipated by that little voice in the back of my head is the size of the 580EX II. I had a feeling the flash was going to throw the camera off balance due to the additional overhead weight on the camera, but I wanted to wait til the flash arrived...
Pros: Very flexible flash angling and output. Well built and very study, weatherproof. Well spaced buttons. Nice green-turquoise back light when light-up button is pressed. Easy open battery compartment.
Cons: Adds significant weight to XTi alone, and causes slight imbalance. Runs on 4 AA batteries instead of providing rechargeable battery option. (Rechargeble option is not stealth). Expensive.
Excerpt: The 580EX II is Canon's top-of-the-line, professional grade external flash and it is packed with features. Accessory flashes are one of the most important pieces of equipment in a photographer's tool bag.
Excerpt: Canon's successor to the might 580EX is heralded only by the addition of a little 'II' after the model number, but brings much in the way of useful improvements. Firstly - and most importantly in my view - weather sealing.
Pros: Power, control
Cons: You're never sure you're getting the most from it
Conclusion: A pesar de ser guia 58 noto con respecto a su par SB700 o 800 que el caudal de luz no esta a la altura de la marca nikon. Veo que esa marca tiene mayor caudal de luz, y muchas más funciones para ajustar a situaciones partuculares.