@sourabh9agrawal, r u sure it is installed with update1?
Note, in SGS the more you talk, the contacts gets stored. It keeps on piling. In my case I could even went back to 20days old phone log.
This makes the phone really slow.
Just clear the log once in a while and it would be fast enough.
U have 4 home screens by default. on second u have daily briefing widget. remove that. It slows down the mobile.
But, seriously I'm on JG4 and the lag is not felt very much. It starts lagging only when the call logs keep piling.
About Kies issue...which OS r u using?
I had XP and Kies just refused to install properly. Its works best in Vista and later