Document management: Google Apps vs SharePoint Online

Resently I have been looking into the options currently available in the document management space, as the members of the local landowners association needs a place to share and collaborate documents.
The requirements are as follows:

• cheap, preferably for free
• should handle MS Office docs
• 5-10 user accounts
• very easy user interface
• web based
• File versioning would be nice
  

This narrows the candidates to just Backpack from 37Signals, Google Apps and SharePoint online, as both MS Skydrive and Google Docs are just a File Share in the cloud and do not offer any collaboration features.

Since I have not been able to locate a free Backpack nor SharePoint offering the Google Apps solution looks like the obvious choice. However I have signed up for a trial version of both Backpack and SharePoint, and I will soon revert with the verdict :-)