All about saving... from Tara

Tara is a member of the Picasa team at Google, who regularly posts to the Picasa Google Groups.  She has just put together what she describes as an info sheet on the new "Save Changes" feature of Picasa 2.5.  The post has been pinned in the group, so that it is easy to find, but unfortunately the Google Groups post only allows for rather limited formatting.  I have taken the liberty of reposting the information here, with rather better formatting (and a couple of spelling corrections!):

Hi all,
I've put together a little info sheet about the new "Save Changes" feature in Picasa 2.5, hopefully this helps clarify how it works :)

• After you upgrade to 2.5, you will notice the new "Save Changes" button on some of your folders. This means the folder contains edited pictures. Rotates are considered edits, and this includes automatic EXIF rotates. Whenever a file in Picasa does not look the same on disk, the "Save Changes" button will be available.
• Saving is not something you need to do. You can use Picasa as you always have, and never save a thing. Picasa will still remember your unsaved edits and allow you to undo/redo them. When you email/blog/etc. from Picasa, your edits will be used. The 'Export' button is also still there.
• Picasa has always kept your original files safe. When you save a file in Picasa, we create an edited copy, and move the original to a subfolder called "originals". The "originals" subfolder is hidden, and will not be visible in Picasa. This automatic backup also allows saves to be undo-able, and revert-able :)
• "Undo Save" brings your picture back to the state is was in before the save - with edits in Picasa, but not on disk. You can undo a save the same way you undo any other edit, by going into the Edit view and using the Undo button. "Revert" will revert your file back to its original state on disk. "Revert" is on the File menu.
• Other tidbits: Save matches the jpeg quality level of the original but, if we can't match it, we use 85%. Non-jpegs are saved as jpegs. If you move an edited file on disk while Picasa is running, the original will move with it. Backup will include saves and originals. Right-click on saved pictures to locate the file or the original on disk. Under the File menu, "Save As..." and "Save a copy" are also available.

In a subsequent post to a followup thread, she also adds

• you can either use [the "Save Changes"] button to save everything in a folder at once OR you can select one picture at a time and go to File > Save.