I believe a "real" photo viewing mode would really make a lot of people happy:
1) Reprocessing of photo on zoom: I think this might be considered a "bug of choice" but as far as I can see, WDTV processes the photos only once when loading to fit on the screen, and then when you zoom in, it zooms into the "scaled-down-&-extremely-sharpened" picture instead of the original file, generating a blurred, upscaled-back output whereas the original file has enough data to fill the screen. Nowadays even many cell phones come with 2.0MP + cameras. Full HD resolution is 2 MP only. So most of the time, when you are viewing a picture/photo, it is scaled down to fit your tv screen (even if it is 1080p) and you don't see the full detail. When you zoom in, you should be getting less downscaling hence moving closer to the original resolution of the picture until you reach %100 (no scaling - the best quality). Only past that point upscaling should start.
And while you are at it, please remove the dreadful sharpening...
Notes: There is an option in the photo settings called "keep as original", but does not work for pictures bigger than the screen and for anyone with a digital camera or a decent cell phone, this is the case all the time.
I have seen this "shortcut" also on other devices. Samsung upscaling DVD player does the same trick, where as if you use the same photos directly on the tv's card reader, you get the perfect "real" picture, albeit being much slower. But there is no point in zooming in if you are not going to see more detail...
2) Zoom buttons: Using two of the buttons for instant zoom in/out instead of going through the menus would be a life saver.
3) Pan buttons: Entering the pan mode instantly once the zoom is active and using the cursor keys for panning would also be perfect (no more menus please).
4) Zoom map: This might be overkill but a little navigation map on zoom would make this complete (a little presentation at the corner marking which part of the picture is actually being viewed)