Watch the demo in Youtube.
Instructions are found here and I can't wait to try it on my phone. Sony recommends it only to experienced developers with extensive knowledge on flashing roms so try it at your own risk. I'm new to flashing roms, and I'm a bit afraid I'll brick my phone. If I do muster the courage to update my Arc S, I'll post the detailed steps here in my blog.
More information at XDA Forum: