What will the cameras be used for

One of the differences stated constantly between the old DS Lite and the new Nintendo DSi, is that the DSi has 2 cameras. However, what exactly will these cameras be used for?
They can of course be used for taking pictures and editing them using software on the DSi. These pictures can then be inserted into any number of applications that you might be using on the DSi. However how about gameplay?

Nintendo have said that one of the major uses will be in gameplay. So does this mean that it might have a wii-like functionality whereby depending on how we move in front of the camera, certain movements will be controlled/affected in the game? Nintendo have been fairly tight lipped so far, and have also not released any games that would have this functionality. However, this does leave the table clear for third parties to develop games and apps that make use of the camera.

One thing is for sure though. There is no way that Nintendo would have spent the extra development funds and time in adding two cameras, if their use was only to take a few pictures here and there.