It seems that there's a cloud everywhere you look, even here in Sunny Florida. For a good overview of the cloud services for file storage and sharing, take a look at this Online Tech Tips
Personally, I use Dropbox, and it's been a really good thing for what I use it for (which is backed-up file storage for my book manuscripts), but in the Tech Tips posting, there are descriptions for the competitors:
Microsoft SkyDrive; Amazon cloud, Apple's iCloud, GoogleDrive. All of these, including DropBox require some action on your part to store files.
For a number of years I used Syncpilicity. This service can work like the others with a set-aside folder, or it can create synchronized file images between your hard drive and its storage. Syncplicity also has some unique arrangements with GoogleDocs, which are by themselves a cloud solution for office documents. For a comparison of Syncplicity and Dropbox, check this out.
But, with all this, there are even more. For example, box.net and of course the major collaboration environments, like SharePoint.
So, you get the point. This subject is endless, and obviously has reached a tipping point, as "cloud" is now a meme
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