From OS X Beta Program:
Known Issues in OS X Yosemite Beta 1
Safari
- Safari may hang when playing certain Netflix content.
iPhoto and Aperture
- iPhoto 9.5.1 and Aperture 3.5.1 are required on OS X Yosemite. Update to these versions from the Mac App Store.
- When entering edit mode in iPhoto, a black screen may be displayed instead of the selected photo.
- Photo Stream and iCloud Photo Sharing may not function properly when both iPhoto and Aperture are installed.
iCloud
- The shared purchase history page on the Mac App Store is disabled for Family Sharing accounts.
- iCloud Drive may appear empty in the Finder after first time setup. Restart to resolve this problem.
AirDrop
- AirDrop may not show nearby Macs.
- Sending files to another Mac using AirDrop may not work.
OS X Yosemite Beta 1 carries build number 14A299l, which is newer than its Developer Preview 4 with carries build number 14A298i.
OS X Yosemite Developer Preview 4 has a lot longer list of known issues.