The Office Web apps Service just got an update. This update brings more features to the Excel and PowerPoint Web apps as well as more optimization for IE9.
New Features:
Excel Web App
You can now insert, delete or rename sheets in a workbook and use familiar tools such as AutoSum and formula assistance.
PowerPoint
It is now possible to change the design theme of your PowerPoint presentation within the PowerPoint Web App.
Just click the Change Theme button to choose from over 45 professionally designed themes. New themes will be added regularly.