What are the differences between a liposome and simple cell membrane
By looking on wikipedia I found: 

About liposome


  A liposome is a spherical vesicle having at least one lipid bilayer. The liposome can be used as a vehicle for administration of nutrients and pharmaceutical drugs. Liposomes can be prepared by disrupting biological membranes (such as by sonication).
  
  Liposomes are most often composed of phospholipids, especially
  phosphatidylcholine, but may also include other lipids, such as egg
  phosphatidylethanolamine, so long as they are compatible with lipid
  bilayer structure. A liposome design may employ surface ligands for
  attaching to unhealthy tissue.


About cell membrane


  The cell membrane (also known as the plasma membrane or cytoplasmic
  membrane) is a biological membrane that separates the interior of all
  cells from the outside environment.The cell membrane is selectively
  permeable to ions and organic molecules and controls the movement of
  substances in and out of cells. The basic function of the cell
  membrane is to protect the cell from its surroundings.
  
  It consists of the lipid bilayer with embedded proteins. Cell
  membranes are involved in a variety of cellular processes such as cell
  adhesion, ion conductivity and cell signalling and serve as the
  attachment surface for several extracellular structures, including the
  cell wall, glycocalyx, and intracellular cytoskeleton. Cell membranes
  can be artificially reassembled.


So the major difference seems to be the presence of "embedded proteins" inside the cell membrane.