The leak is all over the web:
http://sammyhub.com/2013/03/11/pictu...e-galaxy-s-iv/
The major changes are 1080p full hd 5 inch display and 1.8GHz quad core processor. Other features stay more or less the same. More evolutionary than revolutionary IMO.
Galaxy S IV is not for me. In the Android arena, I would only buy a Nexus device. Nexus 5 is rumored to be announced during Google IO in June; I will be waiting for that one.