Here are several undocumented button press combinations that will invoke some useful features and tools. The syntax is to press the number keys shown and then press the "Zones" key...
111 + Zones Puts the Replay in "game" mode after you have entered either "Joshua" or "Tic Tac" into the Claw Foot Portal. (see below on how to access the CFP.)
411 + Zones Shows you information about your ReplayTV box including the serial number, the software version, the most recent connection, etc.
243 + Zones brings up a "utility" menu that lets you force a network connection, toggle a network meter, memory meter, position display, and several other utilities. The bottom of the screen is also the infamous "Claw Foot Portal" (CFP)
382 + Zones On 4xxx series and higher, this lets you reset your ReplayTV to factory defaults. If your ReplayTV becomes unstable, or if you want to resize the photo partition, this is an excellent option. Note: This will erase all shows, ReplayChannels, and Program Guide data! If your ReplayTV box is an earlier model running the 3.x software, use 777 + Zones instead.
243 + Zones While in the Setup Menu lets you modify some IR remote settings letting you control two different Replays with one programmable remote. You can also adjust the HUD transparency. here on older models.
876 + Zones When the machine is next rebooted, this will take you through the full setup process.
887 + Zones While in the Setup Menu, this displays a list of ReplayTV development credits.
888 + Zones While in the Setup Menu, this displays some very funny Haiku poems written by the ReplayTV development team.
999 + Zones on 5080 shows "DownloadQueue requests: ISN" screen. This is a "mockup" of a screen. The data is fake and the same on everyone's box.