Office 2007 and 2010 are "twins" and if you are at ease with 2007, you will feel efficient in next to no time with 2010

• The Office Button has been replaced with a "FILE" tab (in blue) on the Ribbon, that Microsoft has called BACKSTAGE VIEW
  Restructured, some new commands, direct access to help ...
  
  
• New pictures tools
  Remove background
  New artistic effects (sketch, hand drawing or painting ...)
  
  
• Security of the Office files
  Protected View : the source of the file is analyzed. In case of doubt (Internet, attachment opened from within a message) ... and all editing functions are turned off
  It is possible to retrieve the temporary files created by the automatic save function (they are named "versions")
  It is possible to retrieve unsaved files (only during 4 days)
  
  
• Word : few changes
  WordArt type effects applied to characters
  Navigation Pane : looks like the PDF bookmarks Pane - search has been improved
  Forms : you can now create a checkbox control content
  
  
• Excel : also few changes
  Lists : a search textbox has been added to the drop-down filter list (handy when there are lots of criteria)
  Sparkline charts: small charts created inside a cell (in the background and you can type text)
  
  
• PowerPoint
  Sounds and videos are now INCORPORATED inside the presentation (by default)
  Sounds and videos tools : new intuitive tools such as adding a poster frame, adding bookmarks or trimming
  
  
• Outlook : fully new but don't panic ! It is mainly a matter of LOOK, the basic functions behind have not changed ...
  The 2007-2010 Ribbon has been applied to Outlook
  Microsoft tries hard to make Outlook more "open" : you can search a contact from any component, plan a meeting with somebody by simply pointing his/her email address etc ...
  Social networks such as Facebook, LinkedIn, SharePoint ... can be added to the Reading Pane
  A new "conversation" view : I send you a message, you reply to me, I re-reply to you ... all the messages involved are grouped together and you can expand or collapse the conversation as you need