I was having a problem with the Dialog window where it wasn't working with the combination of UI 1.8.12 and Jquery version 1.5.0 when used in IE9.  The Dialog window not only wouldn't fire, it was breaking other Jquery functions on the same page.

 

As soon as I switched to Jquery 1.5.2 the problem went away.  I figured I'd post it here in case anyone else is having a similar problem.