There are a number of iOS apps that make use of Dropbox as a backend storage service and I imagine dropbox buttons in apps would do something similar: anywhere you have an app that needs to store photos or documents they link to your dropbox account to give you an easy in/out method of moving data around.
Yeah we are using Dropbox as syncing / backup in our iOS and Mac budgeting apps currently. To his(Houston's) point, you set it up and then if you throw your phone in the river it doesn't matter. Go get a new phone and you have all of your data.
As space continues to get cheaper, I could see using Dropbox exclusively for storage at some point in the future. Not just a few things I want backed up, but storing everything there. Then any computer I pick up has everything I could ever want or need. Currently it's far too expensive for me to do that though. That is where the real power to "having little Dropbox buttons everywhere" would be for me.
