Windows Live Photo Gallery
Full user review
"Windows Picture viewer was better for viewing photos"
Good for editing, and publishing pictures to social sites easily..
Viewing pictures was easier and less buggy in winXP Picture Viewer, sometimes when you try to enlarge a photo, or even turn it 90 degrees it clicks to the next photo, and several other bugs that haven't been addressed in windows7
I would use it to publish photos to the web easily, and edit them, but would look elsewhere for a tool/program for simply viewing the photos.