A big caution to those updating to iOS 8 early. Unless you can upgrade all your iOS devices, and/or do not depend on iCloud to sync between them and your computer; do not upgrade to iCloud Drive when asked. iCloud Drive is not compatible with old iCloud, and once you upgrade devices on one will not sync with devices still on the other. This goes double for Mac users. Until you update to OS X Yosemite (next month most likely) your iOS devices using iCloud Drive will not be able to sync with your Mac.