Google docs, Zoho, Microsoft Live Skydrive, all excellent products and all provide online storage, and we trust that the provider's filesystems are sufficiently resilient to prevent data loss, though of course there's no way back from accidental deletion (Well Google Docs and Zoho have a trash feature so there's some hope if you realise you've accidentally deleted something), as Aberdeen University found when they went Microsoft and needed to advise students not to save critical work to their skydrive accounts.
And the other problem with all these solutions is that they're online, which can be a problem if you're not at the end of an always on internet connection for whatever reason be it on a plane or thrown out of a coffee shop for loitering and abusing their internet connection.
Well there's two tricks to make a local cache - one, an application to back up files locally is fine if you usually use Google docs but occasionally need a local copy be it because you're offline or just due to healthy paranoia, and the other is to use open office (especially if you prefer to use a local application) and the widget that allows you to push (or pull) files from either Zoho or Google Docs.
And in a more corporate or archival sense, if what you need is a means of providing a means of garnering a copy of files for local archival purposes this will give you one while being able to use the sharing and joint editing features of these environments.
If you're intending to use Google or Zoho as a backing store you need to be fairly disciplined about pushing files up, the paranoia backup application can be wrapped up in a script and run from a cron job, which is ideal if you're backing up to a machine under your desk that's always on ...