Multiple iCloud services are currently experiencing downtime, according to Apple's System Status page, leaving them inaccessible to some users.
Find My Friends, Find My iPhone, iCloud Backup, Contacts, Calendar, Drive, Keychain, Mail, Notes, Reminders, Storage Upgrades, and Web Apps have all been down for some people since 8:35 a.m. Pacific Time.
Back to My Mac, iWork for iCloud apps, Mail Drop, and Photos are also impacted.
Apple's System Status report says that 1.5 percent of users are affected and may be unable to use the above listed services. It's not clear how long the outage will last, but we'll update when it's resolved.
Update: According to Apple's System Status page, the iCloud issue has been resolved.