jQuery 1.5.1 was released a few days ago, fixes a bug in IE9 amongst other minor fixes.
See the blog post @ http://blog.jquery.com/2011/02/24/jquery-151-released/
On top of that, another maintenance release of jQuery UI (1.8.10)
See the blog post @ http://blog.jqueryui.com/2011/02/jquery-ui-1-8-10/