Its hardly 2 months since Samsung launched Galaxy S3. Reports says Android 4.1 Jelly Bean port is out for Galaxy S3 already. The port is just not for normal use, since most of the features are not working. The driver is just under development and may use at your own risk.
There is no news for official firmwares are not out yet. Since unofficial roots are coming we could expect to get the official firmwares soon.
Features like Wi-FI, bluetooth and even camera are reportedly not working on the port. May be you can just check the hardware acceleration and call/SMS features.
Finf more information in http://www.xda-developers.com.