When i got my flash, i was going to get the 430, but Because of the cahback offer, and kerso's very low price, paying a bit more for me to get the 580 was good.
Don't know whether it's worth getting the 580 over the 430, as i don't use it overly often, but it's with me whenever i have my camera bag, but it's been used to get the type of shots that wou;d have been impossable without.