Just bought me one of these, apparently works fine in Galaxy S according to the guys over at XDA.
Is only .5mm in depth than the original but, should hold fine in the SGS as it is.
Lasts 2 days not instead of 1.5. Good increase in battery life. Especially if you want to overclock and still maintain a good days worth of battery.
CLICK HERE - If you fancy buying one yourself
DO NOT BUY THE ONES OFF EBAY - THEY WILL SEND YOU A 1650mAh for the Samsung Galaxy SII - Waste of time and money
I have verified from the link i have supplied, that they work, and also, they are authentic Samsung batteries, it came in a Samsung plastic box when delivered and looks exactly like the one supplied in the picture.