Just got it yesterday and will use it at a wedding tomorrow. I was using the Sigma 500 and while it did a good job, I think the 580ex will do even better. I heard a lot about it being plasticky and flimsy but it does not appear to be any less sturdy than other flash units. It has a nice stylish look to it, being smaller than the 550ex, but I can't yet speak for performance until after this weekend. I will also be using rechargeable batteries (2450mAh) with this flash. In the future I will probably get some type of Quantum battery or similar unit.
Lou