updated 04:47 pm EDT, Mon August 4, 2014
Many changes simply UI refinements
Users are beginning to discover some of the changes in iOS 8 beta 5, which was released earlier today. Many of these appear to affect the Health app. On top of supporting spirometry data, there are for example several new icons, and users can now export the app's information. Privacy settings for the app have appeared within Settings.
Elsewhere iOS is now displaying a pop-up asking for a phone number for SMS Relay. The feature is a part of Continuity, the technology which allows some apps and services to cross over between iOS and OS X.
The Photos app has been improved with a "Last Updated" notification for iCloud sync, and an option to keep full-resolution images in iCloud and smaller files locally. Wi-Fi calling is explicitly identified in the top status bar, and iOS' native keyboard has gained a quick toggle for predictive text.
More changes may be discovered in the next few days. The final version of iOS 8 is due this fall.