Folks,
If you're using this sort of app for "mission critical" material, be sure to read the fine print. Although you can store up to 50 gigs "free for life," no single file can be larger than 100 mb. If you have a massive music library made up of individual songs, that can be useful. But if you're planning to use the service to store, say, movies, you'll find that the 100mb limit won't work for you. In that case you'll have to pay $15 per month for storage (and you'll have access to the storage from your PC or other devices in the bargain.)
That is not to say that this is a bad deal. The $15 per month charge is relatively high compared to some competitors, but it's not outrageous. But "Box" could have offered 500 Gigs "free for life" and achieved the same end. Anyone needing to store anything close to 50 gigabytes of data almost certainly needs to store individual files greater than 100mb in size.