I?m a wedding/event photographer shooting Canon. I grew up with the AE-1 and A1 but graduated to AF Canon as, to be honest, my MF just isn?t good enough for wedding photography. I graduated to digital recently, running it alongside film with a D60. I sold it pretty soon after I had bought it, the AF was inexcusably slow and the flash exposure sucked. A couple of months ago I sold it and traded up to a 10D. The 20D came out that week and the money I saved on the newer body helped to facilitate a 17-40L and 70-200L to go with it. I have had 30X20" prints made from the 10D that equaled my Mamiya 645 for quality. I used to shoot weddings and events with 3 sigma ef-500 super flashes, one on camera and two on stands using wireless ETTL. Portrait shooting was done using the built in light slaves and metering the output as my 2 EOS 50 (Elan II) cameras could not do wireless ETTL with ratios. I used to manage a photo lab, I know what good negs look like, and the flash exposures using that setup were spot on when used with moderate FEC for white dresses etc. With the 10D and the sigmas I realized that I had to work out a system to obtain good exposures. Before I start, in a post below when I complained about the inadequacy of Canon's ETTL, I was recommended to use CF4-1, manually select focusing points to ensure it was on the faces, trade up the 20D and change my sigmas for canon flashes. As far as the first two suggestions are concerned, although, yes it would give me more reliable exposure, I strongly object to having to change to a completely different style of shooting, and especially one which I could not cope with when faced with very fast moving situations which need split second focusing and shooting, such as PJ wedding photography, just to cope with Canon's inadequate flash system. I worked out a system using the sigma flash, that a permanent FEC of - 1/2 stop would in most cases keep the highlights from blowing across all the ISO?s, even when using focus/recompose. However, and I only worked this out last night, when the flip down diffuser or an omnibounce is used on the flash then the camera may overexpose by 2 stops or more! I used the flip down almost always as it stopped the flash head zooming which could be very audibly whiny during a ceremony. With the zoom set manually to 28mm I can still get good exposures plus no noise. However I can still not use an omnibounce. Bounce flash for some reason is still spot on. Oh, another very important point, forget wireless ETTL using the sigma flash on digital. If the master can detect no slave, i.e. it is out of range, then it will blow on full power regardless. With a slave the exposure is wildly erratic to say the least. Please note, this is the case with 2 or 3 sigmas, with a canon and sigma (the canon as master or slave) or with a canon and 2 sigmas, in other words, if you want wireless ETTL with a 10D steer well clear of sigma! (One of them was still under warranty, sigma claimed to have fixed it but I see no improvement whatsoever). I went today to my local pro store to see whether a 550ex was the answer to my problems. Terry, G-d bless him, was one of the guys working there, and he was wearing a black fleece. In other words, the exposure was pretty much the same as if it had been a groom wearing a suit/tux. I focused on his face and recomposed so that the focus point was on his jacket. I shot an entire 1gig card of Terry with the sigma, 550ex and 580ex, using different angles and zooming in/out but keeping the focus point on his jacket. I could have set up a more detailed test, but I don?t shoot dummies at weddings, I needed to know how it would handle real life shooting. I quickly established that I could forget wireless ETTL period whenever a sigma was part of the combination. I also verified that when the sigma was diffused that it overexposed badly, however without it the exposures were definitely good enough at a -1/2 stop (I shoot RAW). The 550ex did not have this problem with the diffuser at all, however the exposures were little different to that of the sigma. The surprise of the evening was that the exposures of the 580ex on the 10D (i.e. no ETTL II) were spot on in almost every frame. (it's also a damn nice flash, and finally as small as Nikon's latest the SB- 800, the feel of it is also a lot better) without any FEC at all. I cannot afford to keep trading up my equipment, I'm trying very hard to make a living, and as I'm in the lower segment of the market I cannot just write off such updates to ?expenses?. I?m sure that a 20D with a 580ex would make me a very happy photographer, but at present I cannot justify the costs, when I am making my sigmas work albeit with a struggle. I could sell two of them and buy a 580ex, but then I lose my slave flashes that are so easy and quick to set up, and that I do my portraiture with when it's too much of a shlep to put up my Bowens. I could buy a 580ex and still have no wireless ETTL, and that?s probably what I will eventually do. Bottom line, firstly congratulations in hanging in there till now! If you are going digital, forget the Sigma EF-500 Super flash, the 550ex is not that much better, but with the price dropping on it, I believe that being able to use an omnibounce and have wireless ETTL, to be well worth the extra, especially if you do not have an investment in sigma flashes. However, even for the 10D, if you can get the 580ex, I really believe that it a big leap as far as ergonomics, weight but most importantly exposure is concerned.