Well the final release of iOS 5 just keeps getting closer, and the folks at Apple are hard at work to make the OS as good as possible, which is why they released the 6th Beta.
While most users are impatiently waiting for the iOS update to go live for everybody, currently it is only officially available to paid devs only at the iOS developer site.
Make sure you read any release notes on-site. Also don’t forget to register your device at the developer portal and prepare it for development before installing the new beta onto pre-beta equipment.
The beta is, as always, released under the terms of Apple’s NDA, so we really can’t tell you much about it.