After updating to the latest 3.1 RC2 build 17315 under Screen Options upon checking and unchecking various Widgets nothing happens. Also, the column options under Screen Layout are non-functioning.
I created a fresh database and install of 3.1 RC2 which had no issues, then immediately after updating to build 17315 I checked the Screen Options panel in the Dashboard and all options are non-functional.
WordPress 3.1 RC2-17315
No plugins activated. No themes installed. Clean install, no content added.