Not strictly about UI testing, but something in that direction: my
(with unittest.js of script.aculo.us, which is also used for the
Prototype unit tests). I'll put up the slides of the presentation
after the talk (so, later this week, maybe Friday or so).
In my experience, for interface and interaction testing itself you'll
have to do manual tests. For example, all browsers known to man have
rendering errors in some situations that you can't really capture
with automated tools-- and while you can tricky with stuff like
screenshot comparisions, this will quickly become extremely tiresome
in this world of quickly changing apps.
The route I'd recommend is: have sane amount of coverage for unit and
libs, and try to have frequent releases. It's imperative that you
check all vital functionality of your app in all supported browsers