Summary: This flash has been great so far. It is an obvious improvement from the built in flash on my 20D, and has made indoor photography infinitely easier in my rather dark 1930's house. While it can't control other flashes, and may lack the additional range of the 580, the price and features were right for my needs.
Pros: Consistent Output, Fast Recycling, Versatile
Summary: I bought this to use with my new super-zoom. I still have much to learn in terms of using and maximizing all of the features but I am still able to get shots that I would never have been able to capture with a lesser flash. After trying the base model Speedlite, I'm glad I went with the larger "horsepower" of this model.
Summary: I liked this flash. Uses disposable batteries. Charge recycles incredible quickly. As powerful as you might want. No need to get a stronger flash. Fits the hot-shoe of my new Canon T2i nicely. Swivels. It is a bit plasticy, but light. Good photos; wouldn't go higher for portraits or parties. A bit pricey nonetheless, but you probably wont replace it anytime soon.
Pros: Consistent Output, Easy To Use, Fast Recycling, Lightweight, Powerful Output, Versatile
Summary: I bought a used Canon 30D a while ago and found out quickly that I needed a real flash. The mini flash that comes with the camera does little but fill in a shot. I have a Canon 10-22 lens that I have fallen in love with and hoped this flash would work really well with, but unless I go up to 14 I get a hard ring of darkness. Overall I do like the flash and I'm sure the longer I use it the more uses I will find for it. But it is not cheap.
Pros: Consistent Output, Durable, Easy To Use, Fast Recycling, Powerful Output, Versatile
Summary: Still learning how to use it. Wish there was a cheaper way to get it off camera (looking at the ST-E2 or Cybersyncs or cord). Contemplated between this and the 580EXII. I think this will be all that I need, as I am just a hobbyist. Its nice to have the ability to bounce now.