AFAIK there is no docs yet, but I learned a lot from the sourcecode, as aways.
One featured that I'm already using is the event delegation functions. They are similar to the functionality provided by the widely known livequery plugin.
jQuery.live(type, fn) is ment to be similar to jQuery.livequery(type,fn)
jQuery.die(type,fn) is ment to be similar to jQuery.expire(live,fn)
But jQuery 1.3 provides this in a much better and performative way, thanks to John! =)
If some of you wish to understand a little about how it works you can look into livequery documentation [ <a href="http://docs.jquery.com/Plugins/livequery">
http://docs.jquery.com/Plugins/livequery</a> ]. But be aware that not all livequery features are covered by 1.3, just the ones mentioned above.
Also, don't forget to look into the previous beta anouncements and at jQuery blog. Some info can be found there.