The cloud is not necessarily the best medium for storing of important files as several recent events have shown. Apple's iCloud services have about 300 million users and several documents stored on them, some critical.
Currently, iCloud services are down for about 3 million of the iOS users (about one percent). Affected users may find it difficult to pull images from photostream, back up apps and data or access documents which are stored from the cloud. In addition, late last night Apple noted that creating new Apple ID's may not be possible for everyone, that issue has since been fixed.
Apple's servers have gone down several times this year, one especially egregious example being the month long developer outage last month which negatively affected several developers causing Apple to offer compensation.The main difference being that the developers outage had limited effects on users while this outage negatively impacts the Apple experience.