jQuery 1.4 Alpha 2 has just been released. The code is a stable release and has been tested in all the browsers they support. The jQuery team are no longer accepting any new features for this release, but rest assured it will be good! Here’s where you can download the code:
The jQuery team need help testing this, so to help them you should use the un-minified version into a live application, a development environment of course, and see if any errors pop up. If you hit an exception or some weirdness occurs immediately login to the bug tracker and file a bug. Be sure to mention that you hit the bug in jQuery 1.4a2!
The final jQuery 1.4 release has been scheduled for January 14, 2010.