The first leak of an Android 4.1.2 Jelly Bean build for Samsung Galaxy S II devices has surfaced. Labeled as build I9300XLSJ, the firmware update was originally posted by XDA Developers forum member izap. The update includes all of the normal enhancements one would expect from a Jelly Bean update like performance improvements courtesy Project Butter, new home screen modes, a new notification bar, and Google Now. Because the file is coming from Samsung, it also includes some of their specific enhancements like the TouchWiz Nature UX interface, access to the Samsung Cloud services, and a couple widgets originally developed for the Samsung Galaxy S III.
The leaked build is prerelease code intended for testing purposes, so it is not supported by KIES and you should probably expect some minor bugs to exist. If you are really anxious to get your hands on Jelly Bean for your Galaxy S II and are willing to live with the possible consequences of flashing your device, follow the source link to download the build and find the directions to get things installed. Otherwise, hang in there and be patient as this seems to be a good indication an official release is on its way to Galaxy S II owners in the near future.