The following comment was so helpful that I thought it would be best served as its own entry… so, without further adieu, Metik from www.metik.com writes in response to “New Look & Feel and Other Notes”:
“Actually, this is not necessarily true–more of a generalization most likely based on your experiences with a specific Photoshop version and the platform it is running on.
You are probably using a version that determines available “Save As” formats based on the current Image mode (e.g. Bitmap, Grayscale, etc.) or you have ran into some type of bug (plugins, particular libraries/DLLs installed, etc.).
On windows based platforms (both Windows XP and Vista) running Photoshop (CS2/8.0 and later), you can definitely “Save As” and choose the PNG format after opening (and even editing) a “flattened” JPG (JPEG) file. Unless you are working with Exif, JFIF, or Motion JPEG, JPEGs do not generally contain multiple layers and are, in a sense, “flattened”.
Although PNG is a great open format, it can take slightly longer to render in IE than some of the more seasoned formats.
If you do you run into a graphic format that is “unsupported” by Photoshop or any other editor for that matter, “XnView” (http://www.xnview.com/) is freely available and can be used to view and convert between several hundred formats.”
