If you do computing, on the cloud or anywhere else, you're using a computer. If you use a computer, there's an OS. The questions you have to ask are (a) can you live with their OS, and (b) does it offer the features you need?

If all you want is file storage with access from anywhere, the OS should be pretty much invisible. You care about the interface to their storage. It's probably designed to be easy to use and to work with any OS you use on your own computers. If you ever want to do anything else, the OS (and the system software they put on top of the underlying OS) will matter a lot. If that's a possibility, I'd suggest you think a bit about your needs down the road.