A Computer User’s Guide to Cloud Storage - NYTimes.com

Check the article link for an overview of cloud services from Google, Microsoft, Dropbox, and SugarSync.  Reviewing the bottom-line summaries for each, it's not clear why Dropbox and SugarSync still exist.

"For those using thumb drives and external hard drives, think of cloud storage as just another way to back up data, but on a remote server. Add in the ability to synchronize and the service becomes even more appealing.
What is different now is the ability to synchronize seamlessly across multiple devices: computers, laptops, smartphones and tablets. And of course, as Google, Microsoft, Dropbox and others compete for your business, the sheer amount of data to be shared and stored continues to expand.
Here is how to start using it right now."

A Computer User’s Guide to Cloud Storage - NYTimes.com