Some common arguments against cloud-based services in general -- and cloud-based file sharing services in particular -- revolve around the security implications of your files getting stored outside your firewall.
A typical argument goes like this: files stored within a public cloud infrastructure that's by definition shared amongst multiple customers cannot be satisfactorily secured. Moreover, you have no control over the geographical location of where files get physically stored. Related concerns also come up around records management, archiving and so forth.
Now, of course there are many myths and red herrings here, and you need to take a candid look at the security of your own data center by comparison. Nevertheless, we find scenarios where enterprises need more control over files than what a cloud-based storage infrastructure can provide.
One way to address this is via a hybrid cloud deployment model. In simple terms, this refers to a model in which you can mix and match the capabilities of public cloud and a private cloud. For example, you may want to keep a highly confidential set of files within your private cloud (or simply your own on-premise storage array), while allowing more generic documents to reside in the public cloud.
And if you remain unconvinced and desire a completely in-house file-sharing and sync solution, ownCloud is an option that you can consider. Unlike other tools, ownCloud does not provide a cloud-based file sharing or collaboration service. Instead, it provides software that you can use to create your own file-sharing or sync service.
Of course you need to account for subtle but potentially quite important variations. For example, some vendors may direct you towards simple on premise storage whereas others favor private clouds.
There are other key distinctions as well. For the real story, check out our full evaluation report.