Using ArcGIS for Desktop 10.1 SP1, I just created a map package (.mpk) from a map (.mxd) which had a Python Add-In (.esriaddin) installed.
When I unpacked the .mpk the .esriaddin was neither installed nor present in the folder that was created in C:UsersGraemeDocumentsArcGISPackages.
Intuitively, I would expect it to be at least present in the package, so am wondering if it that capability has been omitted by accident or design?