Fellow PPT MVPs Glenna Shaw and Luc Sanders have an online tutorial posted on the Microsoft MVP Blog that has great information. See it here.
While the PPT Web App is still limited compared to the full application, it is the best online option available at this point from any of the offerings (and it keeps your PPT file as a PPT file). If you have not tried the PPT Web App, this tutorial walks through the process of setting up the (free) account needed and offers tips on using it.
– Troy @ TLC