Its not going to do anything for you unless you have a Mark III camera. Its weather sealed, 20% faster recycling which is cool but the 580ex is already pretty damn fast.
You only see its true advantages when used with a Mark III
Not really. Weather sealing would benefit older 1D series owners, and there is an integrated PC sync port and thyristor autoflash for non-TTL operation. Couple of other small benefits even for us legacy flash owners. 



Peace be upon you 
