Amazon, Google, and a couple other companies give you free online storage for your personal ebooks and let you read the ebooks in their apps/ereaders. (Another, Libreture, charges 3 pounds per month.)
Another competing service just crossed my desk.
BookFusion is a 3-year-old ebook startup, and one of the things it does is enable organizations and institutions to host and maintain private ebook and document libraries (Bluefire has a similar service). There is also a consumer option which is free at this time.
The neat thing about BookFusion is that you can upload DRM-free Epub ebooks, store them in a personal library, and then use its Android, iOS, and browser app to read them. I'm still testing the system, but it looks nice so far:
With Amazon dominating the ebook market, there will never be a huge market for this idea in the US, although other markets centered on DRM-free or watermarked ebooks (Netherlands, Poland, etc) could use this type of service.
And frankly, so long as Amazon continues to neglect their version of this personal ebook library idea, there will be a market for this.
The thing is, Amazon has been hosting ebooks uploaded by its customers since 2011, but the feature has never been a priority for Amazon and thus has worked very well.
On the Fire tablet, for example, Amazon puts personal ebooks in an entirely separate app called "Docs" rather than including them with all the other ebooks. Amazon also frequently misplaces those personal ebooks (I currently have a half-dozen ebooks on my Fire tablet that I cannot find).
It is annoying enough that I wonder just how many people are reading their own ebooks on Amazon's hardware.