After the jump are a few sample shots comparing the camera performance of the Xperia S and the Xperia arc S. The 12MP Xperia S has to, at the very least, match what the 8MP Xperia arc S can muster but in this comparison, it looks like the Xperia arc S is taking the better pictures.
Having said that, just two samples from each camera are not enough for us to draw a conclusion (though the low light performance on the Xperia S looks better here) and once again, it’s very possible that the Xperia S used here is a pre-production unit. Await the final production version of the Xperia S we shall.
Sample One 100% Crop
Sample Two 100%