I never saw this thread either... Awesomeness!!!
One thing I like do with my flat screen standard CRTs is to use the service mode to change the image size and position. For example, the Neo Geo is kinda zoomed in a bit, so I have to shrink the width and height some. Then you got systems like the PS2 where the image isn't stretched out enough and is off centered to the right a bit. BTW, this comes in handy with games on the NES on the left side of the screen like Mega Man.
The Duo seems to be harder to mess with as some of the image on the top and a lot on the bottom is actually meant to be cut off from the display. The width on the other hand seems to be just right. You will notice that if you shrink the height enough on some games, you will see glitchy moving graphics that are from the top of the screen almost like they sort of connect.
I highly recommend messing the service mode to get desired results. You can fix geometry problems, get more correct colors, etc... I know it is a little OCD having to access it all the time depending on what system you are playing, but it is rewarding to have a perfect image. Just remember that if you don't know what your doing in the menu, you can mess up the settings on your TV. Good news if you use a Sony Wega/Trinitron, it will reset to the factory image if you unplug the TV, unless of course you save the settings with a certain command.