You can get it now, download the profile and follow the instructions linked on this page to get the GM. It's a very slow install but you can speed it up by following these instructions. It took about forty five minutes on mine to install. I'm sure there are lots of changes but the two that have jumped out at me straight away are the new Podcasts app and WebKit - html emails are now displayed correctly. The new face with the multiple complications doesn't appear to be there on my Series 3 but that's not too surprising.