The new PPT viewer was resently released and I have taken the time to run a series of presentations built in different version of PowerPoint to test it. Here is what I have found...
For starters, this viewer isn't like the previous versions; a light weight, quick download. The new PowerPoint 2010 viewer is 60MB! It also needs to be truly installed vs. the previous versions that could be run directly from a CDROM or USB drive. That is a significant down side for taking PowerPoint presentations with you and planning on playing them on any computer with out installing or needing admin rights. Aside from that, there is nothing but praise for the capabilities of what it can do. It handles ALL animations, transitions, trigger events, media, and everything I've thrown at it from all versions of PowerPoint (I tried PPT, PPTX, PPS, PPSX all from multiple versions and languages of PowerPoint). From what I have tested, it runs everything that the full application runs including password protected presentations. You can play and print slides, you just can't edit anything.
You can download the viewer from Microsoft.com here.