Finally, jQuery UI 1.6 final is out, renamed 1.7, and it's on google ajax libraries, so it's minimized (45K for the whole thing; .27 sec to download for me, which is nothing, especially if you're loading at the end of your code so the user is busy reading the content of your site).
The contributors list doesn't include me ($.widget uses $.metadata); so much for my fame and fortune. This release still has the droppable bug; looks like that's to be fixed in 1.7.1.