Can I backup an arbitrary file on iCloud? If I open iCloud in System Preferences, it says I have 5 GB of storage available.  I'd like to use it to back up some zip archives of source code.  Is that possible, or can you only access that storage through specific programs?

Update - I've accepted the answer about the Mobile Backups folder, but I it is not quite what I want for a backup system, so I'm not going to use iCloud for this. If I delete a file from Mobile Backups, it will disappear from the iCloud folder, but I want protection from accidental deletion.  I want plain old file storage.
Yes you can — iCloud can be used to sync anything that you wish.


Open ~/Library/Mobile Documents and create a folder (call it anything you wish).
Inside, put whatever documents you would like to sync over iCloud.
That folder will sync with other Macs (and jailbroken iOS devices, and on the web too if you have a Apple Developer licence).


Alternatively, you can symlink a folder on your Mac in to the Mobile Documents folder so that the files remain in their original location.