As an amatuer with only a 350D I was in two minds whether or not to go for the 580ExII when i could easily have gone for the cheaper 420Ex/430Ex / 550Ex / 580Ex. In the end I decided to future proof and just go with the 580 ExII, I may upgrade my camera body in a number of years, at least I will still be able to use this and all the lenses I have collected so far.
The Canon Speedlite 580EX Flash contains a superset of the features found in the Canon Speedlite 550EX E-TTL Flash in a smaller, lighter and more modern designed housing, although it is still way bigger than the 430Ex. So big it is the biggest peice of equipment in my camera bag! (apart from the tripod of course). Mount this with a 70-300mm tele photo lens and you've got a real workout ahead of you!
It takes 4 normal AA batteries and the flash is on nearly instantly. Recycle time is extremly fast - it was amongst one of the main swinging points for choosing this over the earlier models. I was a bit disspointed with 1700mAh rechargeable batterries although normal alkaline batteries gave me much more flash usage. I might have to try higher value rechargeable batteries like the 2500/2700mAh.
Immediately above the diffuser panel is a white, semi-rigid piece of white plastic (a catchlight reflector) that pulls straight out to create a catchlight in your subject's eyes when using the flash in a vertical bounce position. I never really thought bounce shots would make that much of a difference but boy was I wrong. You get a much better natural light in the shot.
A single button releases both the tilt and rotate locks while a single grip/button press allows the flash head to be rotated and tilted at the same time. Rotation is up to 180 degrees in both directions. I found the tilt very easy to use, even one handed.
One of the other things I liked about this flash is the AF Assist Beam to enhance autofocus in low light conditions, which aligns its beam to the Canons camera focal point and projects itself as a red ir patch on the subject. The white balance is also comunicated directly to the camera too.
Another good point is this flash can be a wireless E-TTL master or a slave when paired up with other speedlites. At the moment I only have one flash, but it means I can opt for the cheaper wireless 430Ex or similar at a much later date when I want to upgrade my setup to include more than one flash, and use the 580 Ex to fire off the slaves automatically.
The hi speed synch, allows the camera to go all the way to 1/4000 second (took me a while to realise I had to set the hi speed synch on the flash, otherwise the fastest shutter speed you'll get is only 1/200 second), although this is at the cost of range / power.
Flash power is great, and I got some really cool pictures using the second curtain sync, although it was more by fluke than anything else! Build quality is super, and both battery door and hot shoe lock can be easily operated with only one hand.
Bottom Line: An excellent flash, may be a bit confusing at first if your a novice/amatuer as I am, but also a bit on the expensive side compared to the 3rd party flashes available for canon. I also found the amazon prices to be very steep - I found this flash a lot cheaper searching around, maybe I bought a grey import, but I've read the imports work just as well as the official ones (as long as you go through reputable sellers) , and so far everyhting works well. On hindsight this flash is probably overkill for the casual photographer - but then this will make sure you experiment more to get the best out of this professional flash!Get more detail about Canon Speedlite 580EX II Flash for Canon EOS Digital SLR Cameras.