Really important to have support for ARIA roles on these types of widgets. That's what they were made for, and jQueryUI does a pretty good job at this.
As the web moves towards richer clients, it is going to be very important for widget developers to keep the web accessible to all. For many sites being accessible is becoming law in some countries (banks, government sites, etc). Also from what I have seen, it is not terribly onerous to add support for ARIA.