This plugin allows you to add photos to your gallery directly from the Picasa interface, via a button added to the Picasa UI.
Please note that this module only allows for the import of images and their filenames. If you want captions (and probably some other bits too), you'll want to take a look at the Picasa Module.
The documentation for the PWU API is available at http://code.google.com/apis/picasa/docs/web_uploader.html.
The module can be obtained from this forum comment.
Extensive credit must go to Timothy Webb, author of the original PublishXP plugin - This module borrows heavily from his code.