Apple has released the next iteration of its iOS 5 beta to developers today. What's changed since Beta 3? You can now update over the air (via Settings -> General -> Software Update), but be warned - the process will delete your precious photos and you'll need to re-sync your device.
Also, as usual, there are also several bug fixes. 9to5Mac is providing the release notes, so check out their post if you want a deep dive into every little detail.
Apple Seeds iOS 5 Beta 4 [9to5Mac]