I've also been using the 580ex, for about 3 years now with excellent results. Exactly what camera settings are you using? There probably is nothing wrong with your 580.... it's likely the manner in which you are using it.
Do you know why the bride's white dress is fine but then everything else goes dark? First off your ETTL is metering for the dress (foreground), so it adjusts flash exposure accordingly, to give you a pleasing result. It sees that bright reflection and shuts down so it's not blown out.
Second, I suspect you are in dark venues, are NOT shooting in manual, and also are probably using higher shutter speeds or apertures that are too small for the desired overall ambient exposure effect that you really want.
You need to allow more ambient light to come into the exposure, to keep everything else from going dark. I choose my ISO first when using flash in dim areas, typically 400 or 800. I make sure my flash is set to MANUAL, and then I will DRAG my shutter speed, around 1/30 sec (really dark room) to maybe around 1/80 (much brighter). This last is a fudge, and you have to play with it to achieve your tastes.
For aperture, I'm around f/5.6 - 8.0, again all depending upon how much ambient light is available, and how much I want to allow in. The flash takes care of the rest, exposing the FOREGROUND.... that is the bride, groom, other folks in group shots, etc. When you settle upon the desired settings, this works perfectly.
In the example below, I wanted to expose for the foreground action in the shot below, which was 1/50 sec, f/6.3 ISO 800. I was fine with the background getting dimmer, as it should for this type of composition, adding a sense of depth.
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