I have only played around with it...but so far, so good.
The flash I had been using was a Braun Vario-zoom...which can be an 'auto' flash...but it only has two setting...F4 and F8. I could still adjust the FE with the ISO slider...but it was a pain at times.
The TTL metering of the Canon unit looks like it will be nice and easy. Being able to use FEC on the camera will be nice.
The Braun was quite powerful for my needs and the 430EX is more powerful yet...so I should be OK for power.
The auto zooming head of the 430 is nice. The Braun has three zoom positions but it has to be done manually...which I often forgot to do.
Comparing the 430 to the 580...the 580 is obviously more powerful, a little bigger and the 580 has much better controls. The 580 has a wheel on the back while the 430 has moon shaped buttons that are skinny and hard to press. If you have FEC on the body, it's not a big deal...but if you have a Rebel or some body without FEC on the body...then the 430 is a pain in the butt. The 580 can be a wireless Master or Slave...the 430 can only be a slave. The 580 is compatible with Canon's remote power pack...I don't think the 430 is. I think that the 580 also twists with more freedom than the 430. The 580 has a pull out deflector card, which my Braun also has...but the 430 doesn't have on...I may miss this feature.