Pycasa is a very helpful and very functional program written in Python to download Picasa photo albums or just the photos (in full resolution) you like the best from a given album. You just have to provide the username, and all the available —public— albums from that user will be presented to you (you can also browse an unlisted album if you have its url).
The program let you download all the photos from one or several Picasa albums, in full resolution, with just one click. You can also browse a given album and choose which photos to download.
Since Pycasa 1.0 you also have the option to log in with your Picasa account and manage your albums: create, edit, delete albums, and upload and edit your photos.
Pycasa provides a super user-friendly PyGTK GUI and it is based on the Google Picasa API.