Although technically the N900/Maemo 5 does support multiple boot animation videos which are played one after another, how many users will really need or want to do that?

If the app uses multiple selection by default, you might confuse the Average Joe user, as they would likely expect the app to work with single selection (as with changing theme etc.). In other words, they would expect selecting a new animation would deselect the previous animation. Having to manually deselect the old animation as well as selecting the new one would be less slick than it could be, and if they neglected to do that and rebooted they would see two videos (both the previously selected one and the newly selected one) played one after the other, and be confused.

If people really want multiple videos to be played, then maybe have it as an advanced option...?