I store all my eBooks in Calibre and Calibre stores them in /Users/<you>/Library/Application Support/Calibre/ and that folder is backed up too with CrashPlan. That is step 1.
With CrashPlan, you can (and should) backup all your data, music and movies automatically on unlimited cloud-storage so your data is backed up outside of your home or work environment. And thus also your eBooks! That is step 2.
And the guys at CrashPlan created an very nice iOS app with which you can access your backup on their cloud-storage from anywhere ... and download files from there onto your iPhone or iPad! And thus also your eBooks! That is step 3.
To illustrate what I mean, I put together an image sequence to illustrates the steps to take to download an eBook from your own backup onto your iPhone or iPad.
Very cool and very handy!
I use this method also when I want to email any file which I have on my desktop at home - I download it from CrashPlan and then email it ... from my iPhone. No need to setup remote login to my iMac, no need to setup screen sharing, etc..
Of course there are other ways, but since this one is completely automatic and also backs up ALL our data, it is my preferred off-site storage solution.
Step 1: Calibre
Step 2: CrashPlan desktop
Step 3: CrashPlan on iPhone
