has there been some discussion on the usage of the DualDisc and DVDplus media formats (what's the difference between those two, anyway?). For me those formats don't really make much sense, since we don't have an entity to apply them to. Basically it's a format were two different media formats (a CD and a DVD) are put onto a single disc.
To properly represent such a release in MB we have to add two MB mediums to the release, one with the DVD and one with the CD side. Like this:
Now is that really an improvement? I don't think so. Technically the individual sides are not in any way special, it's a normal CD and a normal DVD. No player can see any difference. If we apply the DVDplus type to both sides it
a) somehow suggests, that the side is some special format
b) hides the real format of that side (on the example above, which one is the CD, which the DVD)
c) still does not show directly that it is only a single physical disc
So unless we have some way to group several MB mediums according to their physical "packaging" (IMHO this is not much more than a special packaging, one could re-release the same release with two discs and have 100% identical media content) applying the DVDplus does more harm than good.
I agree that it would be useful to represent the dual sided formats in a structured way, but in the current form MB just doesn't provide that. In the meantime I think it is better to use annotations and/or folksonomy tags to mark the affected releases.