In an article by Michael Otey, the top 10 features of the service are suggested to be as follows;

  1. Team Sites
  2. Excel Web App
  3. Work Web App
  4. Outlook Web App
  5. OneNote Web App
  6. PowerPoint Web App
  7. Web desing app
  8. Lync 2010
  9. High availability
  10. Browser based access

For the full story, see http://www.sharepointpromag.com/article/office-365/top-ten-features-office-365-136405http://www.sharepointpromag.com/article/office-365/top-ten-features-office-365-136405