Cloud storage at a personal level can be used as a virtual hard drive for storing documents, notes, PDFs, etc. This becomes especially useful when you have multiple computers and mobile devices. If the documents are in the cloud, you can access them from any device and they’ll always be in sync. The cloud storage apps save them on whatever device you are on then automatically transfer them to the cloud.
For example, I generally write blog posts in a text editor. The file is saved to my Microsoft Skylight local folder. If I go to another computer with Skylight installed, the file will be updated. (If the file was open on that second device and has been changed on the first device, it’ll ask if you want to use the newer version.)
Microsoft Skydrive and Google Drive will store whatever files you want, in whatever order you determine. Evernote, which I use extensively for client notes and scheduling, has a more graphical interface and makes it easy to organize data and then find it. Dropbox also stores documents and is essential for transferring large files, which I do continually with clients.
Ifttt lets you automate transferring files in and out of these cloud storage services (and many others) while Wappwolf focuses on doing this with Dropbox.
All the above services are free, with value-added pay options and work on smartphones too.