In the Picture Viewer:
C - Toggle Actual Size [This overrides all other image effects]
F - Toggle Full Screen <-- forget this for now since Kindle 2 Image Viewer has a bug regarding to full screen mode.
Q - Zoom In
W - Zoom Out
R - Rotate
e = reset zoom level
The 5 way joystick can be used as panning.
P.S. I should have also mentioned that Mangle is great. I guess I have used too many other Swiss-army-knife-like image viewer that preprocess is just too much trouble to go through.