hi there,
as far as I'm aware, fw updates (official ones anyway) for the SGS will come through Kies when your mobile operator has 'skinned' and is happy with their release. This can lead to an update maybe not being available for yourself, but someone on another network may already have their update.
I just kept an eye on my Android news sources and plugged my phone into Kies every now and again to check.
good luck
