Yeah I have actually. It's horrible and really unreliable when document sizes get realistic (40+ pages). Not only that it's so easy to fuck up the document structure badly.

I wouldn't use Excel files on a network. I'd use a database or chuck the xlsx into SVN. Changes to complex data need to be managed. Don't expect miracles. There are edge cases where Google Docs will get this wrong. Sync needs human decisions made occasionally.

See my other comments about usage of SVN/Sharepoint and the use cases.

Office 365 is sharepoint. Skydrive is actually a variety of sharepoint. The interface isn't great but neither is google docs, which is why larger companies tend to just use Sharepoint Workspace which is a desktop app for accessing sharepoint portals.