I was interested to upgrade to 1.8 from 1.7.2, but I found some broken feature with Dialog - set focus to the first tabbable element when dialog is opened.
When dialog is opened, I expect a first button being focused, and such button will process "click" when I press "Enter". It works fine with 1.7.2, but with 1.8 no button is selected when dialog is opened, and therefore "Enter" does not work till you set focus using "Tab" key.
In additional size of buttons are increased despite using the same theme.
This issue actually block me to upgrade to 1.8 and I am waiting for a fix.
I just ran into this issue also. In looking at it though, it might actually be more a bug (or change?) in the way the jQuery .add() function works. When running through the following code it looks as though the add function is not actually appending to the end of the list (like it did in jQuery 1.3.x) but rather inserting into the beginning of the list. This means that when the last ".filter(':first')" is run it is actually picking the uiDialog panel object (the last thing added) rather then any focusable items in it.