Picasa has made excellent decision to NOT modify the original image unless specifically told so by the user.
The previous poster may be unaware that every modification/save cycle will reduce the quality of image stored in the JPEG file (Google/Wikipedia this).
And if you (or you grandma) wants to send the picture, there is email function right in the picasa. On the other hand if you decided to do more serious processing (ex. in Photoshop) your best quality original file is still there.