On 28th of June, Robert Haas committed patch: Dramatically reduce System V shared memory consumption. Except when compiling with EXEC_BACKEND, we'll now allocate only a tiny amount of System V shared memory (as an interlock to protect the data directory) and allocate the rest ...

Some (quite long) time ago, someone, somewhere (my memory is pretty fragile) asked a question. I don't have it exact, but the gist was: is it possible to give some users rights to create new users, without making them superusers, ...