I was doing some playing with the ROKU MediaFly channel, and noticed an option to add content (to MediaFly) via mCodes (MediaFly channel => Content Provider Gallery => Add with mCode => redeem mcode). Of course, the option had no explanation or help, so I did a google search and discovered that mCodes are a little like ROKU's private channel codes, only the content shows up on the MediaFly application itself. While mCodes apparently work for MediaFly applications on a variety of devices, in the case of the ROKU, the new content shows up as new icons at the top most navigation level of the ROKU's MediaFly channel.
Apparently most of the mCodes are still used for testing or private uses, and are kept reasonably secret. However, my search did find a small number of interesting mCodes for the MediaFly ROKU channel:
mCode -- Effect from adding that mCode
twit -- Gives you essentially the ROKU's Twit TV channel, as a sub-channel under the MediaFly channel, without having to separately install the Twit TV channel on the ROKU.
mbox -- Gives you essentially the ROKU's "Motion Box" channel, as a sub-channel under the MediaFly channel, without having to separately install the Motion Box channel on the ROKU.
cnet -- Gives you access to a number of "CNET" videos, as a sub-channel under MediaFly.
mediaflyhd -- This one adds an "HD" MediaFly sub-channel, that appears to be an easy way to browse for MediaFly videos that are all encoded at HD quality.