Using Dropbox to backup iTunes

I'd like to give a few warnings when doing this, assuming you have multiple devices that will be using the same library file from Dropbox.

Firstly, and most importantly, if you're opening the same library on multiple computers at the same time, you're going to get a conflicted copy if there are any changes made.

Most likely there will be changes, namely to the number of plays a certain song has, since that one always changes the moment you finish playing a song. The last thing you'll want is a conflicted copy since you'll get very confused very quickly, and will cause you more hassle than it's worth in the long run.

Secondly, if you're using Mac and Windows, while sharing the same iTunes library, there's a small possibility that there could be incompatibility between the OSes themselves.

Security permissions on Mac might not translate well to Windows, likewise with Windows to other Windows machines. I've experienced this issue with all my iTunes library, and it wasn't even located in Dropbox! External drives, internal drives with different formats (NTFS, HFS, exFAT) all add up to make a mess.

While what you're looking for is possible, bear in mind the above before you start using it!