The sky cleared and trumpets sounded when Microsoft bamboozled the entire cloud storage market by offering unlimited OneDrive storage with certain Office 365 subscriptions.
In addition to bumping up your storage quote to unlimited, they switched the maximum single-file size limit to 10GB (from 2GB). Just when you think you hit the jackpot, you hit an undocumented artificial limit that prevents you from using the all you can eat buffet in the sky.
What is this artificial limit ?
They limit you to 20,000 files total. This means that most users won't get anywhere near the kinds of storage usage scenarios most of us thought Microsoft would be dealing with. Unfortunately most users aren't aware of this. They will start uploading their photo collection and then all of a sudden their agent will stop uploading files. The agent won't generate any errors. Everything will look perfectly fine but they have reached their limit and the game is over.
What about the competition? Dropbox has a statement on this (link) page that says:
Although Microsoft's Office 365 + unlimited storage seems enticing, I would still stick with Dropbox for online cloud storage because it just works better in every way ( faster upload, faster download, no artificial file limits, clients on every platform that work well, etc).