Picasa Web Albums, Picasa Photo Viewer, Retouch tool, albums feature, larger thumbnails...
New in v3.x: Ability to sync your Picasa 3 and Picasa Web Albums edits, Retouch tool, Picasa Photo Viewer, ability to create and edit movies, Text and Watermarking tools, screen capture options, option for printing photo captions; Release Notes - Last Updated: 11.05.09 (v3.5.0 Build 79.81)
New in v2.x: Ability to publish photos to the Web with the new Picasa Web Albums free service, ability to view folders by hierarchy, option to save edits to disk as you go, albums feature for creating virtual groupings of photos, larger thumbnails, improved screensaver, one-click album selection; Release Notes - Last Updated: 11.04.08 (v3.0 Build 57.44 Final)
Pros: Makes pictures readily available for easy editing and sharing, advanced one-click editing features, handily organizes large collections of images, can't complain about the price (it's free)
Cons: Folder structure takes a while to learn and even then can be confusing, initial organization can take a long time if there are many images on your hard drive, saving edited images is cumbersome and counterintuitive,