I use a pretty standard technique for displaying dialogs on an asp.net page.  It is well known that when showing a dialog, it is moved to the bottom of the BODY in the DOM, when in fact it is usually needed inside of the page form (id=aspnetForm usually).  Below is an abbreviated bit of code to show how I accomplish this:

1. function showDialog(id) {
       $(id).parent().appendTo("#aspnetForm");
       //...
   
   
2.     $(id).dialog("open");
   }
   
   
   
   

In 1.7.2, the style attribute of the dialog container dive was set to position it absolutely and calculated correctly to center it.  In 1.8rc1, the dialog is positioned relatively and calculated correctly to center it, but the page renders with a large gap of whitespace at the bottom where the hidden dialog originated, scrollbars appear on the browser, etc., all of the behavior that you don't need and expect. 

Below I am including 2 images of the generated code snippets from Firebug, the first with 1.7.2 loaded, the second with 1.8.rc1.  There were no code changes between these 2 screen shots other than changing references to the library.  I will also attach larger images where these snippets originated.

First the "good" code rendered with 1.7.2:



Now the "bad" code, 1.8rc1:



This is the result of my initial testing from this morning, and otherwise, most things appear to be working well, and smaller dialogs don't necessarily show the user the page gap before the footer, but this is pretty consistent behavior otherwise.