Aside from its Stellarium and Google Sky functions, it has two new features that I found interesting: Viewing the sky from multiple wavelengths and tour guides of celestial objects :D.
On the other hand, the drawbacks of this program are the high PC system requirements (recommended: 2 GB RAM, Core duo processor w/ 2GHz, discrete graphics card w/ 256-VRAM) and a need of DSL connection (its files are in the internet).
Visit Microsoft WWT Website at http://www.worldwidetelescope.org/
Download the program here.
Currently feeling: excited