If you're already familiar with the Arc, all you need to know about the Arc S is that it will be slightly faster. SE is swapping-out the 1GHz Snapdragon the Arc came with for a 1.4GHz model. That makes for a 40% speed increase on paper, and SE says that you can expect real-world performance to amount to about a 20-25% speed-up; that's not world-shattering, but it's a decent bump that should help keep the handset relevant.
The Xperia Arc S is sticking with the Arc's 4.2-inch FWVGA "Reality Display", 512MB of RAM, and 8.1-megapixel Exmor camera. Like the other new Xperias we've heard about, the Arc S will have SE's latest software tweaks, like Facebook inside Xperia, and a 3D sweep panorama mode that lets you use the phone's 2D camera to generate 3D images for viewing over HDMI on compatible displays.
Look for the Arc S to be available in five colors when it comes out this October.
Source: Sony Ericsson