Multibody sheet metal is not something I've had the chance to use a lot. The little of it I've used it seems a little awkward. It's not clear to me what it is meant for. The fact that you can't flatten multiple bodies seems to mean that they don't want you making single part files with multiple finished parts in it. So maybe they meant it to be a transitional state or to work with configurations.
Is anyone out there using multibody sheet metal? What are you using it for?
I think probably the main purpose was to allow the creation of sheet metal parts whereby the process involved creating geometry that wasn't all one body and then eventually hooking them all together into one part. However, the first thing I saw was the ability to mirror the body and not merge it and therefore to have a left and right config of the sheet metal part all in one file. Works ok, but I have had problems show up later in terms of it getting confused about what body to delete, what body to flatten, etc. I hope that is improved in 2011 and will be useful.
WT