I'm on Dropbox for our eBook library and really have no reason to change off of that because it works so well with Calibre. With referrals, I've built up about 14GB of free space so far and have more than enough room. My sons are using the Dropbox accounts for their course lwork also.
Over the past 7 months or so I've been slowly organizing our music library, which is in bits and pieces on 3 different iTunes accounts, plus CDs, plus what we've bought from Amazon or wherever, onto a 2TB external drive and then uploading to the Amazon Cloud. It is very slow work though as I often have to convert to MP3 and then fix all the metadata and then upload it.
Eventually I'd like to just network that external disk to new router and let everybody pull the music either from there or from a Cloud. I haven't had time yet to check out iCloud, but we've lost so many iTunes libraries on crashed computers over the years it isn't even funny. It is really nice to have access to all our purchased songs for re-download now. I bet that when I start combing through the iCloud-s I'm going to find a bunch of songs we own that we don't have on any computer here.