There have been some significant UI changes to Notification Center in iOS 5 beta 2, specifically, the way notifications are handled on the Lock Screen. In beta 1, notifications would simply appear as line items, with new notifications stacking as new line items, one after the other. In beta 2, if a single notification comes in, it now gets its own, newly styled popup.
In both cases, you could and can drag the associated app icon to unlock and be taken directly to the app, only the appearance of the first notification has changed. I addition, Apple has added a visible "window shade" UI element to the lock screen, above the single notification, so you can pull down the full list of recent notifications.
For alarms, the change is even more striking, as the addition of the "snooze" button seemed bitsy in the beta 1 UI but is now big and bold in the beta 2 UI (see above).
The most interesting part of this is that Apple is still working on, or experimenting with, the notifications user experience during the beta process. During previous iOS releases, the user experience for cut, copy, and paste, and for the multitasking fast app switcher and folders remained relatively unchanged during the beta process. (Though significant changes were made prior to the beta period, when it was still internal to Apple).
We know Apple hired the father of webOS notifications over a year ago, but also hired the developer of Jailbreak notifications just prior to the iOS 5 beta release. What, if any, impact that might be having on the betas is unknown, but it's tremendous to actually "see" Apple's design iterations on such a major new feature release.