I'll chime in on this thread as it has been revived and addresses a conversation I had with an IT about this.
From a personal point of view, I think that for solo (self-reliant/independent/self-sufficient/whatever you want to call diving without a buddy) course, I feel that it is important to address entanglements. For some agencies, adding things isn't allowed (PADI, SSI, and possibly others). Some agencies (NAUI for example), allows instructors to add to the curriculum.
My understanding is that many don't want to touch doing this in the open water for liability reasons. If that is the case, I fail to see the point of having students do this in confined water. I teach in the Puget Sound, so I think that for a solo course, this is a fairly good exercise. It is a bit more difficult doing it here in a dry suit and warm undergarments (I'm a wimp when it comes to cold temperatures) than say Guam or similar. If you are in backmounted single or doubles, then you definitely need to have a weight belt on with enough weight so that you don't cork to the surface.
@Trace Malinowski posted a video of him doing this in doubles here:
. You can see the twinset are aluminum cylinders. I think he's in a dry suit, but I can't really tell (Trace? Care to chime in?).
It is something I do want to work on for my on proficiency, even though I'm moving towards sidemount where you don't have so much difficulty in dealing with an entanglement around your valves as compared to having cylinder(s) on your back.